Political Polarization in the U.S. Congress.

Visualizing how the Republicans and Democrats have grown increasingly divided in ideology over the past years.

By Zhe Zhou and Aditya Kundu

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The two parties in power of the U.S. government have been at odds with each other for quite a long time. However, in recent years, political partisanship has had stark detrimental effects.

Deadlocks amongst parties have caused a reduction in the quantity and quality of legislation passed.

The country also saw its longest government shutdown ever at the end of 2018, over a dispute related to the funding of the U.S./Mexico border wall.

It cost the U.S. economy about $3.6 billion and affected 800,000 federal employees.

Let’s understand what went wrong.


Using normalized scores for political ideologies.

To understand patterns in how representatives vote, we are using dw-nominate scores to quantify their political ideology.

Based on a representative’s voting history in Congress, they are assigned a score ranging from -1 to +1 which ranges from extremely liberal to extremely conservative respectively.

These scores are calculated by analyzing roll-call voting patterns and used to investigate trends in party-line voting and party unity.


How does increased polarization affect voting patterns?

Let’s take a look at the democrat, John Conyers Jr.

During the five decades he served in Congress, he voted on 23,829 bills brought to the floor of the House.

He occasionally voted for results that were not favored by his peers in the Democratic party.

However, more recently, he has been strongly aligning with the Democratic party as shown by his voting behavior.

Political polarization does indeed affect the voting behavior of individual politicians and in turn, the entire government.

But which party do I blame?

While the polarization is indeed slightly asymmetric towards Republicans, that does not mean that the GOP is to be directly implicated during government shutdowns.

Taking a closer look at the data, we can understand the right-left shift in more detail.


Adding in another dimension

The next visualization adds another dw-nominate dimension.

This second dimension picks up attitudes on cross-cutting, salient issues of the day (which include or have included slavery, civil rights, regional, and social/lifestyle issues).


Polarization, in politics, refers to the divergence of political attitudes towards extremes.

Republicans and Democrats have always been opposing each other over bills and ideas on what the future of the country should look like. This is how a bi-party parliament works.

However, in recent years, ideological differences in parties have been weaponized in order to win more seats in Congress. Party members are now reluctant to vote across party lines.

Polarization-induced partisan antipathy poses to be a threat to the healthy functioning of a parliamentary system. And with the current trend of increasing polarization, partisanship shall only become more pronounced.