It’s the first day of business for the newly sworn-in 116th Congress, and House Democrats have already held several votes — on a bill to fund the government and a package of rule changes to House procedures. Both passed, but not without some intraparty tension. As the freshly minted majority party in the House, Democrats must wrestle with the question of how they will vote in this era of divided government. Will they vote together against President Trump’s agenda, or will tensions arise between the more progressive and centrist factions of the party, splintering the Democrats’ newfound power?

Time will tell. But with the 115th Congress now in the books, let’s take a step back and look to it for clues. Last session, House Republicans, then in the majority, were largely aligned with Trump — very few broke ranks.

Over the first two years of Trump’s presidency, the average GOP member overwhelmingly sided with Trump — 93 percent of the time in the House and 91 percent of the time in the Senate, according to FiveThirtyEight’s Trump score metric, which tracks how often each member of Congress votes with the president. Trump’s position isn’t clear on every vote, so this analysis covers only 96 votes in the House and 84 in the Senate. This is only a small subset of the more than 1,800 votes cast in Congress during the 115th session.

Democrats largely voted against the president’s positions, but they weren’t quite as unified against Trump as Republicans were for him: In the House, the average Democratic member agreed with Trump 23 percent of the time; in the Senate, 31 percent of the time.

The voting behavior we saw in the 115th is pretty much what we’d expect. Because Republicans controlled both the executive and legislative branches, they were more likely to vote in unison on issues and avoid bringing votes to the floor that would be divisive or unsuccessful — although that certainly wasn’t always the case. Times when Republicans broke ranks and voted against the president — like a few did in July 2017 on legislation that would have repealed parts of the Affordable Care Act — drew attention, but votes like those weren’t the norm. The three GOP senators who sank the health insurance bill — Susan Collins of Maine, the late John McCain of Arizona and Lisa Murkowski of Alaska — all had Trump scores of 75 percent by the end of the 115th Congress.

Now that Democrats control the House — and which bills come to the floor — we’d expect to see more party cohesion. There’s also the possibility, now that government is divided and House Republicans are no longer responsible for passing bills, that more GOP members will step out of sync with the president.

But Trump’s approval rating might have to take a nose dive before Republicans defect. While it’s unclear how voting patterns will shift in the new Congress, what is particularly striking is just how effective Trump has been in securing party loyalty in the first two years of his presidency. As you can see in the chart below, Senate Democrats didn’t coalesce as neatly around Obama during his first two years in office as Senate Republicans did around Trump.

George C. Edwards III, a political science professor at Texas A&M University, has collected historical legislative data from previous presidencies, comparing the president’s stance on a bill with how a senator voted on it. Specifically, Edwards captured how a senator voted on “contested” legislation — bills on which the winning side received less than 80 percent of the vote. (This metric isn’t exactly the same as our Trump score, so the chart above limits the votes its using to Edwards’ “contested” criteria.) On these votes, the average Republican voted with Trump 96 percent of the time, while the average Democrat voted 90 percent of the time with Obama’s position in his first two years. That may be because Trump’s White House and GOP leaders in Congress are more skilled legislative stewards or because of the sorts of bills that made it to the floor. It may simply be because times are more partisan now.

Increased partisanship is at least part of the explanation; you can see that in how the opposition voted in Obama’s and Trump’s first two years. Not only did Trump’s Republicans support him more consistently than Obama’s Democrats did him, but Democrats opposed Trump more consistently than Republicans did Obama. The average Democrat voted 17 percent of the time with Trump’s position, while the average Republican voted 20 percent of the time with Obama’s.

Whether this trend will continue in the Senate in years No. 3 and 4 of the Trump presidency is unclear. Some Republican senators, such as Mitt Romney, have publicly criticized the president, but it’s too early to tell if such rhetoric will translate to more Republicans voting against the president, like some did in the vote to end U.S. military support in Yemen.

But don’t fret — you can follow along for yourself: We’ve updated our Trump score interactive to include the new members of the 116th Congress, and it shows how often they vote in line with the president (or how often they don’t).





FiveThirtyEight’s 2020 draft, episode 1