How we got here: the issues that divided the parties, 1790s to today

Historical setting

In the 46th Congress, which opened in 1879, the average Republican and the average Democrat in the House stood 0.786 apart on the scale political scientists use to place members by their votes. In the 80th Congress, which opened in 1947, the distance was 0.523. In the 119th Congress, which opened in 2025, it was 0.910, the largest in the record. The Senate followed the same path: 0.748 in 1879, a low of 0.472 in 1941, and 0.923 in 2025 voteview.comvoteview.com.

The scale is DW-NOMINATE, built from every recorded roll-call vote. Voteview, the project at UCLA that maintains it, describes its first dimension as the one that through most of American history has separated "liberal" from "conservative," also called "left" and "right" voteview.com. The chart below plots, for each Congress, the Republican average minus the Democratic average on that dimension, using Voteview's published party averages voteview.comvoteview.com. Underneath it, each row shows an issue, the years it divided the parties, and what each party said or how its members voted, with a source for every line.

Source: Voteview: Congressional Roll-Call Votes Database (Lewis, Poole, Rosenthal, Boche, Rudkin, Sonnet), Congressional Parties data voteview.com. For each Congress from the 46th (1879) on: the mean DW-NOMINATE first-dimension score of the Democratic (party code 100) and Republican (party code 200) members, per chamber, from the nominate_dim1_mean column. -1 is the most liberal score on this scale, +1 the most conservative. The year shown is the first year of each Congress. The current Congress is in progress.

Show the numbers

Congress	Year	House Democrats	House Republicans	Senate Democrats	Senate Republicans
46	1879	-0.391	0.395	-0.453	0.295
47	1881	-0.395	0.388	-0.449	0.315
48	1883	-0.347	0.377	-0.449	0.311
49	1885	-0.366	0.384	-0.446	0.298
50	1887	-0.37	0.395	-0.459	0.289
51	1889	-0.384	0.412	-0.453	0.312
52	1891	-0.341	0.425	-0.441	0.311
53	1893	-0.351	0.44	-0.438	0.323
54	1895	-0.422	0.416	-0.423	0.346
55	1897	-0.389	0.43	-0.426	0.381
56	1899	-0.364	0.437	-0.418	0.397
57	1901	-0.369	0.448	-0.374	0.399
58	1903	-0.364	0.45	-0.361	0.434
59	1905	-0.38	0.445	-0.367	0.436
60	1907	-0.36	0.438	-0.361	0.426
61	1909	-0.353	0.427	-0.361	0.417
62	1911	-0.325	0.414	-0.31	0.407
63	1913	-0.308	0.404	-0.281	0.407
64	1915	-0.314	0.41	-0.285	0.422
65	1917	-0.308	0.408	-0.279	0.419
66	1919	-0.311	0.405	-0.293	0.425
67	1921	-0.31	0.395	-0.286	0.421
68	1923	-0.289	0.407	-0.253	0.414
69	1925	-0.281	0.395	-0.269	0.398
70	1927	-0.286	0.382	-0.273	0.392
71	1929	-0.284	0.369	-0.278	0.403
72	1931	-0.256	0.36	-0.227	0.367
73	1933	-0.251	0.331	-0.208	0.332
74	1935	-0.256	0.305	-0.208	0.297
75	1937	-0.256	0.314	-0.228	0.267
76	1939	-0.249	0.308	-0.22	0.254
77	1941	-0.258	0.313	-0.218	0.254
78	1943	-0.249	0.302	-0.195	0.292
79	1945	-0.265	0.303	-0.219	0.275
80	1947	-0.237	0.285	-0.192	0.293
81	1949	-0.276	0.277	-0.239	0.267
82	1951	-0.262	0.28	-0.2	0.276
83	1953	-0.253	0.278	-0.192	0.287
84	1955	-0.279	0.277	-0.23	0.28
85	1957	-0.283	0.268	-0.234	0.268
86	1959	-0.296	0.267	-0.272	0.256
87	1961	-0.277	0.262	-0.278	0.269
88	1963	-0.292	0.256	-0.291	0.278
89	1965	-0.301	0.246	-0.297	0.28
90	1967	-0.296	0.243	-0.299	0.253
91	1969	-0.31	0.255	-0.289	0.251
92	1971	-0.311	0.254	-0.287	0.233
93	1973	-0.323	0.261	-0.326	0.265
94	1975	-0.315	0.265	-0.325	0.271
95	1977	-0.306	0.267	-0.32	0.269
96	1979	-0.301	0.295	-0.313	0.277
97	1981	-0.3	0.307	-0.299	0.311
98	1983	-0.302	0.326	-0.301	0.307
99	1985	-0.309	0.334	-0.306	0.314
100	1987	-0.309	0.335	-0.294	0.314
101	1989	-0.313	0.34	-0.293	0.323
102	1991	-0.314	0.345	-0.299	0.32
103	1993	-0.334	0.371	-0.296	0.338
104	1995	-0.361	0.397	-0.302	0.351
105	1997	-0.376	0.402	-0.31	0.374
106	1999	-0.373	0.404	-0.295	0.364
107	2001	-0.377	0.41	-0.295	0.369
108	2003	-0.376	0.417	-0.292	0.358
109	2005	-0.387	0.423	-0.308	0.378
110	2007	-0.368	0.439	-0.295	0.392
111	2009	-0.349	0.456	-0.309	0.397
112	2011	-0.393	0.467	-0.3	0.444
113	2013	-0.384	0.482	-0.326	0.47
114	2015	-0.394	0.48	-0.333	0.476
115	2017	-0.388	0.489	-0.335	0.487
116	2019	-0.372	0.5	-0.343	0.499
117	2021	-0.379	0.503	-0.352	0.526
118	2023	-0.384	0.508	-0.351	0.544
119	2025	-0.386	0.524	-0.367	0.555

MyHistory

Which moments shaped you most?

History is personal. Pick the moments that shaped what you think, put them in order, and keep your list. Change it whenever what you learn changes your mind.

The voters moved too. In 2014 the Pew Research Center reported that 92% of Republicans were to the right of the median Democrat, up from 64% twenty years earlier, and that 94% of Democrats were to the left of the median Republican, up from 70% in 1994. The share of each party with a very unfavorable view of the other more than doubled over the same period pewresearch.org.

What follows is the record, era by era, then issue by issue. Each era has its own chapter.

1790s to 1865: the first parties to the Civil War

The one thing that changed everything: the Kansas-Nebraska Act, May 30, 1854. Senator Stephen Douglas's bill let settlers in the new Kansas and Nebraska territories decide whether slavery would be legal there, in land where the Missouri Compromise of 1820 would have outlawed it. The National Archives states that the act "aggravated the split between North and South on the issue of slavery until reconciliation seemed virtually impossible," that its opponents "helped found the Republican Party," and that as a result "the United States moved closer to civil war" archives.gov.

The first party fight was over money and the Constitution. In 1791, with a bill to establish a national bank before President Washington, his secretary of state, Thomas Jefferson, and his secretary of the Treasury, Alexander Hamilton, gave him opposite written opinions. Washington sided with Hamilton avalon.law.yale.eduavalon.law.yale.eduloc.gov. Hamilton led the Federalists loc.gov. The opposition, led by Jefferson, became known as the Democratic Republicans senate.gov.

"To take a single step beyond the boundaries thus specially drawn around the powers of Congress, is to take possession of a boundless field of power, no longer susceptible of any definition." avalon.law.yale.edu

Thomas Jefferson, secretary of state, leader of the Democratic-Republican opposition, opinion on the national bank, 1791

"That every power vested in a government is in its nature sovereign, and includes, by force of the term, a right to employ all the means requisite and fairly applicable to the attainment of the ends of such power." avalon.law.yale.edu

Alexander Hamilton, secretary of the Treasury, Federalist leader, opinion on the national bank, February 23, 1791

After Andrew Jackson won in 1828, his supporters became the Democratic Party and his opponents, led by Henry Clay, called themselves Whigs senate.gov. When the Whig Party broke apart over slavery in the 1850s, a new Republican Party replaced it, a coalition formed to block the spread of slavery into the western territories senate.gov. By 1856 the two parties that still contest elections today had written opposite answers into their platforms.

"Congress has no power under the Constitution, to interfere with or control the domestic institutions of the several States, and that such States are the sole and proper judges of everything appertaining to their own affairs." presidency.ucsb.edu

Democratic Party, national platform, June 2, 1856

"it is both the right and the imperative duty of Congress to prohibit in the Territories those twin relics of barbarism--Polygamy, and Slavery." presidency.ucsb.edu

Republican Party, national platform, June 18, 1856

On January 31, 1865, the House passed the Thirteenth Amendment, which ended slavery, 119 to 56. Every Republican who voted said yes, 84 members. Democrats voted 14 yes and 50 no voteview.com.

Read the chapter: The first parties to the Civil War, 1790s to 1865.

1865 to 1932: Reconstruction to the New Deal

The one thing that changed everything: the end of Reconstruction, 1877. After the disputed election of 1876, a commission with a Republican majority gave the contested electoral votes to the Republican, Rutherford B. Hayes. The House historian states that Hayes then effectively ended Reconstruction "by reducing the number of federal troops in the region and doing little to protect the civil and political rights of African Americans" history.house.gov. By 1877, the same source states, the Democratic Party, "led by many of the same officials who had sparked the secession movement and fought for the Confederacy, had regained control of southern state governments," and Democrats then carried out "a coordinated policy of discrimination, intimidation, and violence to block Black political participation and undermine the Republican Party in the South" history.house.gov.

Before that, on June 13, 1866, the House accepted the Senate's version of the Fourteenth Amendment, including its definition of citizenship, 137 to 37. Republicans voted 127 to 0. Democrats voted 0 to 37 voteview.com. Two years later the parties put their positions on Reconstruction into their platforms.

"We regard the reconstruction acts so-called, of Congress, as such an usurpation, and unconstitutional, revolutionary, and void." presidency.ucsb.edu

Democratic Party, national platform, July 4, 1868

"The guaranty by Congress of equal suffrage to all loyal men at the South was demanded by every consideration of public safety, of gratitude, and of justice, and must be maintained." presidency.ucsb.edu

Republican Party, national platform, May 20, 1868

The same decades produced fights over tariffs, Chinese exclusion, prohibition and woman suffrage. On several of them, majorities of both parties voted the same way: the Chinese Exclusion Act of 1882, the prohibition amendment of 1917, the immigration quota law of 1924 voteview.comvoteview.comvoteview.com. By the 72nd Congress, which opened in 1931, the distance between the parties had fallen to 0.616 in the House and 0.595 in the Senate, from 0.739 and 0.717 in 1911 voteview.com.

Read the chapter: Reconstruction to the New Deal, 1865 to 1932.

1932 to 1968: the New Deal to civil rights

The one thing that changed everything: the Civil Rights Act of 1964. On February 10, 1964, the House passed it 290 to 130, and Democrats from the eleven former Confederate states voted 7 yes and 86 no voteview.com. On September 16, 1964, Senator Strom Thurmond of South Carolina changed his party to Republican senate.govsenate.gov. The full story is in the New Deal to civil rights.

What came first: the Great Depression and the New Deal. The House historian states that "by the 1930s, the Great Migration and the Great Depression would transform the northern wing of the Democratic Party." Black workers generally benefited from New Deal jobs programs, and Black voters nationwide began leaving the Republican Party. In 1934 Arthur Mitchell, a Chicago Democrat, defeated the Republican Oscar De Priest and became the first Black Democrat elected to Congress. The House historian states that his victory "signaled the beginning of a long-term shift in Black political allegiance to the Democratic Party" history.house.gov.

In 1936, after three years of the New Deal, the parties wrote opposite verdicts on it.

"On the foundation of the Social Security Act we are determined to erect a structure of economic security for all our people." presidency.ucsb.edu

Democratic Party, national platform, June 23, 1936

"America is in peril. The welfare of American men and women and the future of our youth are at stake." presidency.ucsb.edu

Republican Party, national platform, June 9, 1936

In Congress the lines were less clean. The Social Security bill had passed the House in 1935 with 77 Republican votes for it and 18 against voteview.com. The House historian dates consistent Black Democratic voting to the late 1940s history.house.gov. This era holds the lowest party distances in the whole record: the Senate in 1941 and the House in 1947 voteview.com.

Civil rights divided the Democrats by region. On February 10, 1964, the House passed the Civil Rights Act 290 to 130. Democrats voted 152 to 96 and Republicans 138 to 34. Democrats from the eleven former Confederate states voted 7 yes and 86 no voteview.com. In the Senate, a coalition of 27 Republicans and 44 Democrats ended the filibuster on June 10, and the bill passed June 19 senate.govvoteview.com. President Johnson signed it on July 2 senate.gov.

"We have talked long enough in this country about equal rights. We have talked for one hundred years or more. It is time now to write the next chapter, and to write it in the books of law." presidency.ucsb.edu

Lyndon B. Johnson, Democrat, president, address to a joint session of Congress, November 27, 1963

"Stronger than all the armies is an idea whose time has come." senate.gov

Everett Dirksen, Republican, Senate minority leader, quoting Victor Hugo in the cloture debate, June 10, 1964

On September 16, 1964, Senator Strom Thurmond of South Carolina, who had run for president in 1948 as the States' Rights Democratic candidate, changed his party to Republican senate.govsenate.gov.

Read the chapter: The New Deal to civil rights, 1932 to 1968.

1968 to 2000: the great sort

The one thing that changed everything: Roe v. Wade, January 22, 1973. The Supreme Court held that the right of personal privacy "is broad enough to encompass a woman's decision whether or not to terminate her pregnancy" law.cornell.edu. No Democratic or Republican platform had used the word abortion before 1976; from 1980 on, the two platforms took opposite sides presidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edu. When the Court overruled Roe in 2022, its majority wrote that "far from bringing about a national settlement of the abortion issue, Roe and Casey have enflamed debate and deepened division" supremecourt.gov.

In the 87th Congress, which opened in 1961, Voteview's records list 105 Democrats and 8 Republicans who served in the House from the eleven former Confederate states, and 22 Democrats and 1 Republican in the Senate. In the 119th Congress, which opened in 2025, the same states have sent 46 Democrats and 102 Republicans to the House and 4 Democrats and 20 Republicans to the Senate voteview.com.

In 1976 the Republican platform described a party divided on abortion presidency.ucsb.edu. By 1980 both platforms had taken a side.

"The Democratic Party supports the 1973 Supreme Court decision on abortion rights as the law of the land and opposes any constitutional amendment to restrict or overturn that decision." presidency.ucsb.edu

Democratic Party, national platform, August 11, 1980

"we affirm our support of a constitutional amendment to restore protection of the right to life for unborn children." presidency.ucsb.edu

Republican Party, national platform, July 15, 1980

The 1980 Republican platform also dropped the party's endorsement of the Equal Rights Amendment, which it had been the first party to endorse, in 1940 presidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edu. In the House the party distance rose in every Congress from 1977 to 1995, from 0.573 to 0.758 voteview.com.

Read the chapter: The great sort, 1968 to 2000.

2000 to now: today

The one thing that changed everything: September 11, 2001. Three days after the attacks, the House voted 420 to 1 to authorize force "against those responsible for the recent attacks launched against the United States": Republicans 214 to 0 and Democrats 204 to 1 clerk.house.gov. Congress created the Department of Homeland Security, which opened on March 1, 2003 dhs.gov. On October 10, 2002, the House authorized force against Iraq 296 to 133, with Republicans 215 to 6 and Democrats 81 to 126 clerk.house.gov.

On March 21, 2010, the House passed the Affordable Care Act 219 to 212. All 219 yes votes were Democratic; 34 Democrats and all 178 Republicans voted no clerk.house.gov. In 2011 the House distance passed its highest level from the 1890s, and in 2017 the Senate did the same voteview.com. The 2024 platforms took opposite positions on people living in the country without legal status.

"Congress must pass legislation to provide a pathway to citizenship for Dreamers, farmworkers, careworkers, and other long-term undocumented individuals who contribute to this country, by paying taxes and contributing to their local economies." presidency.ucsb.edu

Democratic Party, national platform, August 19, 2024

"President Trump and Republicans will reverse the Democrats' destructive Open Borders Policies that have allowed criminal gangs and Illegal Aliens from around the World to roam the United States without consequences." presidency.ucsb.edu

Republican Party, national platform, July 8, 2024

Read the chapter: Today, 2000 to now.

Religion across the eras

Religion runs through every era of this record, and it has its own chapter: Religion and the parties. The chapters cover Protestant, Catholic, Latter-day Saint, Jewish, Muslim, Hindu, Buddhist and Sikh Americans, and Native American religions. Three rows of the chart touch religion directly: the 1856 Republican platform's pairing of "Polygamy, and Slavery," the 1876 fight over public money for sectarian schools, and school prayer after 1962 presidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edulaw.cornell.edu.

In Pew Research Center data for 2023, 59% of Protestant voters and 52% of Catholic voters identified with or leaned toward the Republican Party, as did three-quarters of Latter-day Saint voters and 85% of White evangelical Protestant voters. Sixty-nine percent of Jewish voters and 66% of Muslim voters identified with or leaned toward the Democratic Party. Pew reports a 20-point rise over three decades in the share of White evangelical voters aligned with the Republicans pewresearch.org.

Issue by issue

Each row of the chart, in brief.

Slavery. In 1848 the Free Soil Party ran under the banner "Free Soil, Free Speech, Free Labor, and Free Men" presidency.ucsb.edu. In 1852 the Whigs accepted the Compromise acts, "the act for the recovery of fugitive slaves from labor included," as "a final settlement" presidency.ucsb.edu. Republicans declared in 1860 that "the normal condition of all the territory of the United States is that of freedom" and in 1864 called for an amendment to "terminate and forever prohibit the existence of Slavery" presidency.ucsb.edupresidency.ucsb.edu. Democrats in 1864 called the war "four years of failure to restore the Union by the experiment of war" presidency.ucsb.edu. The Senate passed the Thirteenth Amendment on April 8, 1864, 38 to 6; all 31 Republicans who voted said yes, and Democrats voted 2 yes and 5 no voteview.com.

National bank and tariffs. Vetoing the bank's recharter in 1832, Andrew Jackson wrote: "It is to be regretted that the rich and powerful too often bend the acts of government to their selfish purposes" avalon.law.yale.edu. The 1840 Democratic platform said "congress has no power to charter a national bank" presidency.ucsb.edu. The 1844 Whig platform called for "a well-regulated currency" and a tariff with "protection of the domestic labor of the country" presidency.ucsb.edu. Republicans backed protective tariffs from 1860 and called protection "the bulwark of American industrial independence" in 1896 presidency.ucsb.edupresidency.ucsb.edu. In 1892 Democrats called it "a fraud, a robbery of the great majority of the American people for the benefit of the few" presidency.ucsb.edu. In 1993 House Republicans voted 132 to 43 for NAFTA and House Democrats 102 to 156 against clerk.house.gov. In 2024 the Republican platform called for "baseline Tariffs on Foreign-made goods," and the Democratic platform opposed "extreme import tariffs" while citing "strategically increasing tariffs" on products from China presidency.ucsb.edupresidency.ucsb.edu.

Reconstruction and civil rights. In 1892 Democrats pledged "the defeat of the Force Bill," a federal elections bill, while Republicans demanded that every citizen, "white or black," be allowed "one free and unrestricted ballot" presidency.ucsb.edupresidency.ucsb.edu. In 1948 the Democratic platform said minorities "must have the right to live, the right to work, the right to vote, the full and equal protection of the laws" presidency.ucsb.edu. The States' Rights Democrats answered: "We stand for the segregation of the races and the racial integrity of each race" presidency.ucsb.edu. In 1964 both platforms pledged to enforce the new Civil Rights Act presidency.ucsb.edupresidency.ucsb.edu. In the Senate vote, Democrats split 46 to 21 and Republicans 27 to 6; Senator Barry Goldwater of Arizona voted no voteview.com.

Immigration and nativism. The American Party of 1856, the Know Nothings, declared that "Americans must rule America" presidency.ucsb.edu. In 1876 the Democratic platform called for legislation to "prevent further importation or immigration of the Mongolian race," and in 1880 both parties called for restricting Chinese immigration presidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edu. The 1882 law suspended the immigration of Chinese laborers for 10 years and was not repealed until 1943 history.state.gov. House Democrats voted for it 102 to 3 and Republicans 88 to 34 voteview.com. The 1924 quota law, which gave visas to two percent of each nationality counted in the 1890 census and excluded immigrants from Asia, passed the House with Democrats 158 to 37 and Republicans 163 to 33 history.state.govvoteview.com. The 1965 Immigration and Nationality Act conference report passed with Democrats 202 to 60 and Republicans 118 to 10 voteview.com. The 2024 Republican platform promised the "LARGEST DEPORTATION OPERATION IN AMERICAN HISTORY" presidency.ucsb.edu.

Alcohol and prohibition. Both parties supplied majorities for the prohibition amendment: in the House, Democrats 140 to 64 and Republicans 138 to 62; in the Senate, Democrats 36 to 12 and Republicans 29 to 8 voteview.comvoteview.com. In 1932 the Democratic platform said "We advocate the repeal of the Eighteenth Amendment" presidency.ucsb.edu. The Republican platform said prohibition "was supported and opposed by members of both great political parties" and proposed an amendment letting states decide presidency.ucsb.edu. On February 20, 1933, House Democrats voted 179 to 32 to send repeal to the states and Republicans 109 to 89 voteview.com.

Women's suffrage and equal rights. The Progressive Party pledged in 1912 "to the task of securing equal suffrage to men and women alike" presidency.ucsb.edu. In 1916 both major parties endorsed suffrage but left it to the states presidency.ucsb.edupresidency.ucsb.edu. The Nineteenth Amendment passed the House on May 21, 1919, with Republicans 200 to 19 and Democrats 102 to 70, and the Senate on June 4, with Republicans 36 to 8 and Democrats 20 to 17 voteview.comvoteview.com. It was ratified August 18, 1920 archives.gov. Republicans endorsed an equal rights amendment in 1940 and Democrats in 1944 presidency.ucsb.edupresidency.ucsb.edu. In 1980 the Republican platform said "We acknowledge the legitimate efforts of those who support or oppose ratification of the Equal Rights Amendment" presidency.ucsb.edu.

Labor and the New Deal. The 1932 Democratic platform advocated "unemployment and old-age insurance under state laws" presidency.ucsb.edu. The Social Security Act passed the Senate in 1935 with Democrats 60 to 1 and Republicans 15 to 5 voteview.com. In 1947 Congress passed the Taft-Hartley labor law over President Truman's veto: in the House, Republicans 225 to 11 and Democrats 106 to 71; in the Senate, Republicans 48 to 3 and Democrats 20 to 22 voteview.comvoteview.com. The 1948 Democratic platform called for its repeal; the Republican platform listed "a sensible reform of the labor law" among the accomplishments of the Republican Congress presidency.ucsb.edupresidency.ucsb.edu.

Church and state. In 1876 the Republican platform recommended an amendment "forbidding the application of any public funds or property for the benefit of any school or institution under sectarian control." The Democratic platform called the question "the false issue with which they would enkindle sectarian strife in respect to the public schools" presidency.ucsb.edupresidency.ucsb.edu. On June 25, 1962, in Engel v. Vitale, the Supreme Court held that "it is no part of the business of government to compose official prayers for any group of the American people to recite" law.cornell.edu. The 1964 Republican platform backed a constitutional amendment allowing religious exercise in public places, and the 1980 platform backed "voluntary, non-denominational prayer in schools" presidency.ucsb.edupresidency.ucsb.edu. In 2016 the Republican platform urged "the repeal of the Johnson Amendment"; in 2024 the Democratic platform said "we will maintain the separation of church and state" presidency.ucsb.edupresidency.ucsb.edu.

Abortion. No Democratic or Republican platform used the word abortion before 1976 presidency.ucsb.edupresidency.ucsb.edu. The 1976 Republican platform said "There are those in our Party who favor complete support for the Supreme Court decision which permits abortion on demand" and others who sought "a constitutional amendment prohibiting all abortions" presidency.ucsb.edu. The 1976 Democratic platform called it "undesirable to attempt to amend the U.S. Constitution to overturn the Supreme Court decision" presidency.ucsb.edu. On June 24, 2022, in Dobbs v. Jackson Women's Health Organization, the Court held that "Roe and Casey are overruled" and that "the authority to regulate abortion is returned to the people and their elected representatives" supremecourt.gov. In 2024 the Republican platform said "After 51 years, because of us, that power has been given to the States and to a vote of the People," and the Democratic platform said "we will pass national legislation to make Roe the law of the land again" presidency.ucsb.edupresidency.ucsb.edu. In a Pew survey in January 2026, 63% of Republicans and Republican leaners said abortion should be illegal in all or most cases, and 84% of Democrats and Democratic leaners said it should be legal in all or most cases pewresearch.org.

Guns. The 1968 Republican platform called for "legislation to control indiscriminate availability of firearms, safeguarding the right of responsible citizens to collect, own and use firearms for legitimate purposes" presidency.ucsb.edu. The 1968 Democratic platform cited "a new gun control law," and the 1972 platform called for "a ban on sale of hand guns known as Saturday night specials" presidency.ucsb.edupresidency.ucsb.edu. In 1980 the Republican platform said "we oppose federal registration of firearms" presidency.ucsb.edu. The Brady bill passed the House in 1993 with Democrats 184 to 69 and Republicans 54 to 119; the 1994 assault weapons ban passed 216 to 214, with Democrats 177 to 77 and Republicans 38 to 137 voteview.comvoteview.com. On June 26, 2008, in District of Columbia v. Heller, the Court held that "The Second Amendment protects an individual right to possess a firearm unconnected with service in a militia" law.cornell.edu. In 2021, 81% of Democrats and 20% of Republicans told Pew that gun laws should be stricter pewresearch.org. In 2024 the Democratic platform said "We will once again ban assault weapons and high-capacity magazines," and the Republican platform listed "THE RIGHT TO KEEP AND BEAR ARMS" among its promises presidency.ucsb.edupresidency.ucsb.edu.

Police, crime and policing. In 1968 the Republican platform said "Lawlessness is crumbling the foundations of American society," and the Democratic platform pledged "a vigorous and sustained campaign against lawlessness in all its forms" and an "attack on the root causes of crime and disorder" presidency.ucsb.edupresidency.ucsb.edu. The 1994 crime bill conference report passed the House 235 to 195, with Democrats 188 to 64 and Republicans 46 to 131, and the Senate with Democrats 54 to 2 and Republicans 7 to 36 clerk.house.govvoteview.com. On June 25, 2020, the House passed the George Floyd Justice in Policing Act 236 to 181, with Democrats 233 to 0 and Republicans 3 to 180 clerk.house.gov. The day before, a Senate cloture vote on taking up the JUSTICE Act (S. 3985) failed 55 to 45, short of the three-fifths required, with Republicans 52 to 1 and Democrats 2 to 43 voteview.com. The 2020 Democratic platform called for "banning the use of chokeholds and carotid holds" and "reining in the doctrine of qualified immunity" presidency.ucsb.edu. The 2024 Republican platform pledged to "restore Law and Order" presidency.ucsb.edu.

Same-sex marriage. The Defense of Marriage Act passed the House on July 12, 1996, 342 to 67, with Republicans 224 to 1 and Democrats 118 to 65 clerk.house.gov. The 2004 Republican platform said "anything less than a Constitutional amendment, passed by the Congress and ratified by the states, is vulnerable to being overturned by activist judges" presidency.ucsb.edu. The 2012 Democratic platform said "We support marriage equality" presidency.ucsb.edu. On June 26, 2015, in Obergefell v. Hodges, the Court held that "Same-sex couples may exercise the fundamental right to marry" law.cornell.edu. The 2016 Republican platform condemned "the Supreme Court's lawless ruling in Obergefell v. Hodges" presidency.ucsb.edu. The Respect for Marriage Act passed the Senate with Democrats 47 to 0 and Republicans 12 to 36, and the House with Democrats 219 to 0 and Republicans 39 to 169 voteview.comclerk.house.gov. In May 2025 Gallup measured support at 88% among Democrats and 41% among Republicans, a 47-point gap it called the largest since it began asking 29 years earlier news.gallup.com.

Climate and environment. On September 22, 1970, the Senate passed the air quality standards bill, H.R. 17255, 73 to 0, with 43 Democrats and 30 Republicans voting yes voteview.com. In July 1970 President Nixon signed Reorganization Plan No. 3, which called for an Environmental Protection Agency, and on December 2, 1970, the Senate confirmed William Ruckelshaus as its first administrator epa.gov. The 1972 Republican platform listed the agency among the administration's new organizations presidency.ucsb.edu. The Clean Air Act Amendments of 1990 passed the House 400 to 25 and the Senate 89 to 10, with majorities of both parties voteview.comvoteview.com. The 2008 Republican platform said "common sense dictates that the United States should take measured and reasonable steps today to reduce any impact on the environment" presidency.ucsb.edu. The 2009 House climate bill passed 219 to 212, with Democrats 211 to 44 and Republicans 8 to 168 clerk.house.gov. The 2016 Republican platform said "Climate change is far from this nation's most pressing national security issue," and the 2024 platform said "We will DRILL, BABY, DRILL" presidency.ucsb.edupresidency.ucsb.edu. The 2024 Democratic platform pledged "To tackle the climate crisis" presidency.ucsb.edu. In 2023 Pew reported that 78% of Democrats and 23% of Republicans called climate change a major threat, and that the Republican figure was almost the same as ten years earlier pewresearch.org.

Health care. The 1948 Democratic platform favored "a national health program for expanded medical research, medical education, and hospitals and clinics" presidency.ucsb.edu. The 1964 Republican platform accused the administration of using federal authority "to force a compulsory hospital program upon the people and the Congress" presidency.ucsb.edu. The 1965 hospital insurance program for the aged, part of the Social Security Amendments of 1965, passed its final House vote with Democrats 237 to 48 and Republicans 70 to 68, and its final Senate vote with Democrats 57 to 7 and Republicans 13 to 17 voteview.comvoteview.com. The 2008 Democratic platform said every American should "be guaranteed affordable, comprehensive healthcare" presidency.ucsb.edu. The Affordable Care Act passed the Senate on December 24, 2009, 60 to 39, with 59 Democrats and one independent voting yes and 39 Republicans voting no voteview.com. The 2012 Republican platform called it "the fiscal nightmare of Obamacare" presidency.ucsb.edu. On January 19, 2011, the House voted to repeal it 245 to 189, with Republicans 242 to 0 and Democrats 3 to 189 clerk.house.gov.

Issues that changed sides

• Tariffs. Republican platforms backed protective tariffs from 1860 and Democrats opposed them in 1892. In 1993 most House Republicans voted for NAFTA and most House Democrats voted against it. In 2024 the Republican platform called for baseline tariffs presidency.ucsb.edupresidency.ucsb.educlerk.house.govpresidency.ucsb.edu.
• Civil rights for Black Americans. Republicans voted unanimously for the Thirteenth and Fourteenth Amendments in the House and Democrats mostly or entirely against voteview.comvoteview.com. In 1948 the Democratic platform adopted a civil rights plank and the States' Rights Democrats left over it presidency.ucsb.edupresidency.ucsb.edu. In 1964 both parties gave majorities to the Civil Rights Act, and most of the no votes were Southern Democrats voteview.comvoteview.com. The South's members of Congress went from mostly Democratic in 1961 to mostly Republican in 2025 voteview.com.
• The Equal Rights Amendment. Republicans endorsed it first, in 1940, and dropped the endorsement in 1980 presidency.ucsb.edupresidency.ucsb.edu.
• The environment. The Senate passed the 1970 air bill with no votes against, and the 1990 Clean Air Act Amendments drew majorities of both parties. The 2009 House climate bill drew 8 Republican votes voteview.comvoteview.comclerk.house.gov.
• Gun legislation. The 1968 Republican platform called for legislation on the availability of firearms; the 1980 platform opposed federal registration presidency.ucsb.edupresidency.ucsb.edu.
• Abortion. No Democratic or Republican platform used the word before 1976. In 1976 the Republican platform described both views inside the party. From 1980 the platforms took opposite sides presidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edupresidency.ucsb.edu.
• Issues once shared. Chinese exclusion, prohibition, the 1924 quotas, the 1965 immigration law, the Social Security Act and the Defense of Marriage Act each passed with majorities of both parties voting yes voteview.comvoteview.comvoteview.comvoteview.comvoteview.comclerk.house.gov.

Evidence

The polarization series uses Voteview's Congressional Parties file, which gives the mean first-dimension DW-NOMINATE score of each party's members in each chamber in each Congress voteview.comvoteview.com. Democrats are party code 100 and Republicans party code 200, the same codes Voteview's own polarization article uses voteview.com. The series starts with the 46th Congress (1879 to 1881) and ends with the 119th (2025 to 2027), which was still in session when the file was downloaded on October 30, 2026.

• House: 0.786 in 1879; 0.739 in 1911; 0.523 in 1947, the lowest; 0.565 in 1971; 0.758 in 1995; 0.860 in 2011; 0.910 in 2025, the highest voteview.com.
• Senate: 0.748 in 1879; 0.717 in 1911; 0.472 in 1941, the lowest; 0.520 in 1971; 0.653 in 1995; 0.744 in 2011; 0.923 in 2025, the highest voteview.com.
• Highest values before 1913: 0.838 for the House (1895) and 0.815 for the Senate (1899). The House passed that level in 2011 and the Senate in 2017 voteview.com.

Party vote counts by member come from Voteview's roll-call records and from the House Clerk's votes-by-party tables. Paired and absent members are not counted as yes or no. The Southern counts cover members who served at any point in the Congress from Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas and Virginia, including replacements, so they can exceed the number of seats voteview.com.

What the evidence does not show

DW-NOMINATE measures how members of Congress vote. It does not measure what voters believe, and a distance on the scale is not a count of issues. The opinion figures come from surveys of the public and are reported here for the years each survey was taken.

A platform states what a convention adopted. It does not show how many of the party's members agreed, and it does not bind how they vote. The vote tables show how members voted on one roll call each; other roll calls on the same bills sometimes split differently.

The record lists what each party said and how its members voted. It does not establish why any member or voter changed parties. Where a source states a cause, the text says so and cites it.

Sources

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