One of Donald Trump’s regular complaints during his presidency was that Democrats, unlike Republicans, were more likely to stick together in important votes on Capitol Hill. As was the case with many things Trump said, the observation was rooted more in what he wanted to see happen — Republicans falling in line to support what he wanted — than in studied consideration of what was actually happening.
But with Republicans ready to take control of the House and the contest to elect a speaker more unusually fraught, we thought it would be worth assessing whether there was any truth to Trump’s claim, however inadvertently.
To assess this question, we pulled vote data from the past 10 congresses, from the start of the 108th Congress in 2003 to the most recent votes in the 117th, taken on Wednesday. For each vote, we calculated the total number of votes cast by Democrats and the total number by Republicans, as well as the majority position of the caucus (or, in rare cases, the plurality). That allowed us to calculate a metric we’ll call party conformity: the percentage of votes from a party that aligned with the majority position.
So let’s say that there were 220 votes cast on a bill by Republicans. Of those, 200 were “yea” votes. That would mean that the GOP had 91 percent party conformity on that vote. By assessing those numbers over time, we can figure out how often each party’s members voted with the majority — or, considered in reverse, how often members went sideways on the rest of their caucus.
In the House and the Senate, the average party conformity score was higher for Democrats than Republicans over the nearly 18,000 total votes taken. Democrats in the House voted with their party 90.4 percent of the time; Republicans in the House, 89.3 percent of the time. In the Senate, the gulf was wider: Democrats lined up 89.8 percent of the time while Republicans did so only 86.6 percent of the time.
If we sort the values into buckets — conformity of 0 to 9 percent, 10 to 19 percent, etc. and then up to 90 to 99 percent and 100 percent — you can see that Democrats consistently had more votes in which they displayed more loyalty. The further to the right you go on the chart below, the more often the blue Democratic column is taller — meaning more votes in which Democrats had higher conformity.
(A quick note here to mention that this includes only party members. So Sens. Bernie Sanders (I-Vt.) and Angus King (I-Maine) are excluded from the Senate numbers for Democrats, for example.)
If we break out those votes with more granularity, we get a better sense of where the parties diverge — and don’t. In the House, the most common conformity percentage for each party was 97 percent, after which point the figures started to drop again. In the Senate, the most common percentage was 98 percent (in part because the smaller chamber is less likely to see votes in which the caucus can be broken out into 97 percent versus 3 percent).
In the House, Republicans were more likely to have conformity of 97 or 98 percent than were Democrats — but Democrats were more likely to have conformity of 99 or 100 percent … and 95, 94, 92, 91, 89, 88, etc. percents.
By now you’ve realized that there’s another important factor to consider: the chamber majority. After all, it’s not a big deal if Republicans go south on a bill if the party is already going to lose, a consideration that helped define the right-wing fringe of the GOP’s House caucus over the past two years.
When we compare conformity to the number of votes taken by the party — an effective way of measuring majority status over time — we see that Democrats still are more likely to vote on party lines. On the charts below, the blue dots are consistently above the red dots, meaning that even when the two parties are casting the same number of votes on a bill, the Democrats tend to show more party unity.
Also remember that this is an assessment of two decades of votes. This predates the Trump era; it even predates the tea party. Over the past 20 years, Democrats have, in fact, been more likely to stick together on votes than have Republicans.
It’s something that is causing House Minority Leader Kevin McCarthy (R-Calif.) no small number of headaches as he tries to cobble together votes from his caucus to earn election as House speaker. In general, the 118th Congress will be defined by the GOP’s very narrow majority, meaning that conformity will be more important than ever. But on one of the first votes the House will take, a small number of Republicans going sideways could make the difference in how history remembers Kevin McCarthy.