The good folks at Voteviewblog* have been putting together real-time ideal points (estimates of ideological positions, based on roll call votes) for members of Congress in recent days. In a recent post (via Bernstein), they note that, despite media coverage to the contrary, the Democratic Party is not in danger of any sort of a crack-up right now. In fact, the party has been growing more ideologically homogeneous in recent years.

It’s a great catch, but it also kind of buries the lede. What’s really notable is that, in the past few years, the Democrats in Congress have become more ideologically homogeneous than the Republicans, for the first time in like ever. The chart below plots the standard deviation of ideal points in the U.S. House by party since 1861.

As the chart shows, the Democrats, up until recently, have pretty much always been more ideologically diverse than the Republicans. And at least since the New Deal, it’s not hard to understand why. For a while, the Democratic Party was the party of both Southern conservatives and Northern liberals. Then it became the party of African Americans and whites, urban and suburban voters, environmentalists and union members, etc. It has traditionally been the more aggressive party in terms of incorporating new voters and enfranchising immigrants. Basically, its voters have usually been more diverse, so it’s not surprising to see that its elected officials were more diverse, as well. This was the idea behind Will Rogers’ famous quote, “I am not a member of any organized political party. I am a Democrat.”

But that’s changed in recent years. As Southern and rural whites have continued to abandon the Democratic Party, it has grown ever more ideologically cohesive, while the Republicans have actually become somewhat more ideologically diverse during the rise of the Tea Party movement.

So when Donald Trump recently complained, “The weakness of conservatives is that they destroy each other, whereas liberals unite to win,” he was actually on to something.

*Kudos to Jeff Lewis, Nolan McCarty, Keith Poole, and Howard Rosenthal for updating the DW-NOMINATE program and providing regular updates on the data.

[Cross-posted at Mischiefs of Faction]

Seth Masket

Seth Masket is an associate professor of political science at the University of Denver.