# Evolution of political polarization in the US Congress

    This essay is on Wikiversity to encourage a wide discussion of the issues it raises moderated by the Wikimedia rules that invite contributors to “be bold but not reckless,” contributing revisions written from a neutral point of view, citing credible sources -- and raising other questions and concerns on the associated '“Discuss”' page. It links to an appendix containing a tutorial on how to create the plots discussed in this article. That tutorial makes updating these plots completely reproducible as long as the data source web site is not changed in a way that breaks the code. The tutorial is an R Markdown vignette compatible with the RStudio integrated development environment. Both RStudio and the R statistical software are free and open source with versions available for Microsoft Windows, macOS, and Linux.
This article discusses the evolution of political polarization in the U.S. Congress in the post-Reconstruction era, 1879-2023 using the latest data from the Voteview website and other sources. The appendix links to an R Markdown vignette, which should make it relatively easy for anyone to reproduce and update the figures in this article provided they have access to the Internet and a computer running versions of Windows, macOS, and Linux, supported by the R project for statistical computing.
Voteview has coded all roll call votes by members of the US House and Senate since the first Congress began in 1789, when George Washington was President. These roll call votes and other data have been combined and condensed into "Liberal-Conservative" scores for each member of Congress.

## Ridgeline plot of the distribution of Republican and Democratic members of the US Congress since 1879, the end of Reconstruction, following the American Civil War

Figure 1 extends a "ridgeline plot" both backward and forward to 1879-2023 from 1963-2013. This plot shows the two parties becoming more polarized from 1879 to 1895 and 1905 then coming together during World Wars 1 and 2 and the Great Depression. The convergence ends in 1947, but the two parties do not diverge much until 1969. Since then, the Republicans have mostly become more Conservatives and the Democrats more Liberal, though over three quarters of the divergence has been due to Republicans becoming more Conservatives.

## Evolution of the difference between average scores of Republican and Democratic members of the US Congress

Figure 2 shows the evolution of the difference between the average lines in Figure 1. This difference increases from 1897 to a rough plateau between 1895 and 1905. Then the averages for the two parties converge through World Wars 1 and 2 and the Great Depression until 1947. Since 1947, they've generally been drifting apart, though the rate of increase in this measure of political polarization has generally been much greater since 1969.

### Possible drivers

The following have been mentioned as major contributors to this increase in political polarization:
* Republican Southern Strategy to convert racist Southern Democrats into Republicans, visible especially in Figures 1 and 2 starting in 1969, Richard Nixon's first year as President.
* Moves by major corporations to buy the major commercial broadcasters, fire nearly all the investigative journalists and replace them with the police blotter. The public thought that crime was out of control, though there had been no substantive increase in crime. They voted in a generation of politicians promising to get tough on crime, and the incarceration rate increased by a factor of almost 5 in the 25 years between 1975 and 2000 after having been relatively stable for the previous 50 years between 1925 and 1975. And income inequality began to increase, as the power of organized labor declined, and the ultra-wealthy captured most of the increases in productivity reflected in the growth in average annual income (Gross Domestic Product, GDP, per capita) in the US. This strategy has been copied in other countries, e.g., by Vincent Bolloré in France.
* The end of the Fairness doctrine in 1987, contributing to the rise of Conservative talk radio. Figure 2 shows a slight reversal of this trend in 1999, a result of the 1998 United States House of Representatives elections during which the Republicans lost 4 seats. Newt Gingrich resigned as Speaker.
* The rise of Facebook and Internet companies, especially social media, starting in 2004.
The last three of these are discussed in more detail in "Information is a public good: Designing experiments to improve government".
Since 2011, this polarization has been the most extreme since 1879, the end of Reconstruction, and has been getting worse.

### Discourse regarding the attack on the US Capitol January 6, 2021

An indication of the extent of this polarization was the action of Republicans in the US House and Senate to explicitly defund a Working Group established by Secretary of Defense Lloyd Austin to make recommendations for how to root out violent extremists from the US military. Current and former military participated in the attack on the US Capitol, January 6, 2021, and the 1995 Oklahoma City bombing, to name only two such incidents. Mr. Trump as President pardoned Dwight and Steven Hammond, whose arson conviction was a primary motivation for the 2016 Occupation of the Malheur National Wildlife Refuge, during which law enforcement killed one of the lead organizers as he was reaching for a handgun concealed in a pocket.
Mr. Trump has said "he will free Jan. 6 rioters on first day if re-elected", and we can expect Republicans in the US Congress to support such actions.
These actions by Republicans in Congress and Mr. Trump have not occurred in a vacuum. Shortly after the January 6, 2021, attack, "a small but growing number of Republican lawmakers" were claiming that those demonstrators were nonviolent. Comments of this nature were challenged by so-called liberal media. However, with Fox and other conservative networks telling their audiences that the 2020 election had been stolen from Trump, and with many social media feeds making money from similar claims, Republican elected officials in the US House and Senate opposed efforts to root violent extremists out of the military, leading to provisions of the National Defense Authorization Act passed in December 2023 and 2022 to defund Austin's Working Group devoted to that issue, as noted above. At a Univision town hall October 16, 2024, Trump insisted that January 6, 2021, was a "day of love" for his supporters, with "Nothing done wrong." Yet over 1,000 people have been convicted with roughly 350 trials still pending including over 100 people charged with using a deadly or dangerous weapon or causing serious bodily injury to an officer, according to January 2024 numbers from the Justice Department. If you believe Trump, then you presumably also believe that none of these people got a fair trial.

### Implications for voters in the November 5 US federal election

If you want the President to pardon all those involved in the violent attack on the US Capitol on January 6, 2001, vote for him. If you think the US military should recruit, train and encourage violent extremists, vote for only Republican candidates for the US Congress. On the other hand, if these prospects concern you, vote only for Democrats for President and the US Congress.

### Overconfidence and exploitation by media

Everyone thinks they know more than they do, and media organizations exploit that to please those who control most of the money for the media. This is visible in the settlement on the lawsuit Dominion Voting Systems filed against Fox: The rules of evidence in the court of public opinion is whatever will please those who control most of the money for the media. The rules of evidence in US courts tend to be more balanced. In 2023, Fox agreed to pay Dominion $787.5 million, over three quarters of a billion dollars, while admitting that they had originally reported that Biden had won the 2020 election but switched to avoid losing audience to rival conservative networks. That $787.5 million was a tax deductible cost of doing business and was less than 6% of Fox's 2022 gross. Thus, if Fox had a 6% larger audience for a year, they made money lying to their audience even after paying Dominion $787.5 million.
But it's not just Fox. In February 2016, Les Moonves, then Chairman of CBS, said the Trump campaign "may not be good for America, but it's damn good for CBS ... .The money's rolling in and this is fun". All the major commercial media have a conflict of interest in honestly reporting on election campaigns and politics more generally, including giving Trump extra coverage, because he attracts an audience.

### Talking politics

Fortunately, individuals can leverage their concerns by talking politics with others. A famous study of the 1940 presidential election found that people who had changed their mind about whom to vote for said they were most influenced by other people, not the media. This is a general principle that has stood up to replication.
You can encourage others to follow your lead by talking politics -- with humility and respect. You may wish to ask others if you can share your opinion. If they agree, do so without raising you voice and respectfully inviting their response.

## Average scores of Republican, Democrat, Northern and Southern Democrat members of Congress

Figures 3 and 4 are updates with minor revisions of plots of mean difference between Republican and Democratic members of the US House and Senate created byPolitical Science professor Jeff Lewis at the University of California, Los Angeles. Figure 5 superimposes Figures 3 and 4 on the same plot. Figure 6 extracts only the Republican and Democratic information from Figure 5, ignoring the difference between Northern and Southern Democrats.

## Appendix. Companion R Markdown vignette

Statistical details that make the research in article reproducible are provided in an R Markdown vignette on "Evolution of political polarization in the US Congress/plots".
This combines modifications of code from two sources:
* Figure 1 was produced by code written after studying the code used to produce an earlier Ridgeline plot in Friendly and Wainer (2021).
* Figures 3-6 in this article were produced after studying code dating from 2018-02-01 by Jeff Lewis, available on GitHub.