Have Democrats or Republicans Become More Radical? This Data has the Answer.
There is an ever-present discussion among voters in the US. Republicans are certain that they are the moderates, and that the Democrats moved so far to the left that Republicans now look far-right to Democratic eyes. On the other side, Democrats are certain that it is Republicans who’ve rushed to the far-right, and that their own moderate positions suddenly appear like far-left battlecries.
You can make both points by cherrypicking certain topics, but that is not what I want to do here, because even for this question, the answer lies in publicly available data.
Contents
How the median ideology of Democrats and Republicans shifted
Divergence
Conclusions
Republicans Moved Far to The Right In Past 40 Years
VoteView tracks the ideological score of every single US House member and Senator on a scale from liberal (-1) to conservative (+1), using roll call voting data and the NOMINATE system created by political scientists Keith T. Poole and Howard Rosenthal (the system, in part, analysis roll call votes). Compiling all scores of House members of one party together leaves you with a median ideological score for that party at a particular point in time. The great part is that VoteView has tracked this data for each US Congress dating back to formation of the two party system over 100 years ago, so we can get a timeline of how the major parties shifted ideologically. Before we take a look at historic shifts, let’s answer our leading question: Which party has drifted away from the center the most in the past 40 years? The answer: Republicans.
The median ideological score of Democrats has only slightly moved left, from -0.32 in 1977 to -0.40 in 2025. At the same time, the Republican Party has moved far to the right. Their ideological score has more than doubled from 0.26 to 0.53. The result is the polarization gap - the ideological difference between the two major parties - jumping from 0.58 in 1977 to 0.93 in 2025. Republicans are responsible for about three-quarters of that increase. While Republicans in 1977 could argue that they were narrowly closer to the center than Democrats, they are today 0.13 points further away from it than their opponents.
In historical terms, the Democrats are just as liberal as they were in the 1920s. There was a period in time when the average House Democrat became much more centrist, but this was mainly due to Southern Democrats clinging to segregation (many of these Democrats abandoned the party after the civil rights movement, and white southerners are now the backbone of the Republican Party). Republicans also had a period of moderation during the civil rights era. But starting with Nixon’s presidency, who famously resorted to racist sentiments to win over the South, Republicans moved away from the center at an astoundingly steady pace.
That reality has not made its way to the voters. In a recent CBS/YouGov survey, 58% of Americans said that the Republican Party was too extreme, and 49% said the same about the Democratic Party. That comes despite the fact that the House Democrats have barely moved ideologically in the past 100 years, while Republicans have.
But what about the progressive Democrats calling for unprecedented ideas that even many of their colleagues view as too liberal? It is correct that there are a lot of differences among Democrats, but the party is closer together on the NOMINATE ideology scale than Republicans. In the 119th Congress (the current one), Republicans are stretched out on the x-axis, which measures ideology: Some members are moderates like their Democratic counterparts, but the dots on the grid you can find below stretch out to the conservative edge.
Democrats, on the other hand, are not stretched out horizontally, but vertically. The vertical axis “2nd dimension” measures not ideology, but divergence on secondary issues, such as social issues like Civil Rights. In polarized times, the gaps here have dwindled, as cross-party voting became rare. You can explore this timeline vizualisation to see how extensively members of congress used to stretch out on the y-axis as they frequently voted with the other party. While the y-axis does not measure loyalty, it still presents us with an informative picture.
Republicans unwavering bind and loyalty to Trump as well as their fear of his primary powers might explain the lack of fluctuation they have on the y-axis. The outlier is Thomas Massie, a conservative who was not afraid to buck Trump on many secondary issues like the Epstein Files. Massie just lost his primary to a Trump backed challenger.
On the Democratic side, there is still some eagerness to break with party expectations. Unsurprisingly, progressives like Alexandria Ocasio-Cortez, Rashida Tlaib and Ilhan Omar are at the bottom of that group, often breaking with their party, even as their ideologies broadly align. If you are into the math of this method, which I tried to understand and explain to my best abilities here, you can read up on detailed methodology and data analysis at VoteView.
Conclusion
The first conclusion is that the US has become incredibly polarized. 40 years or even 30 years ago, members in the scatter plot you see above used to overlap with the other party and were stretched out vertically, as cross-party voting was still the norm. Now, the parties are strictly separated, with very few moderates left. Here are all my conclusions about the current congress:
House Democrats are morde moderate than House Republicans.
Seven Democrats and five Republicans are within the very centrist -0.2 to 0.2 range. Three of these 12 representatives might lose re-election in 2026. A fourth, Jared Golden (D-ME) is retiring.
Republicans have 12 “hardliners” while Democrats have zero. This means 12 Republicans have a score of >0.8 while no Democrat exceeds -0.8 pts on the ideological scale
Democratic voting behavior, particularly among progressives, is less bound to the party than Republican voting behavior.
If you should even run into someone trying to argue about extremism or a leftward shift within the Democratic party, this is the data to prove them wrong.
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