Donald Trump promised to come to Washington and get government working again. But the stunning failure of President Trump and Paul Ryan’s first legislative priority, the American Health Care Act, reveals that he underestimated a unique fracture of the modern Republican Party. Yes, moderate and very conservative Republicans were against the AHCA for very different reasons, making it difficult to find common ground. But there was also a second fissure that helped to take down the American Health Care Act. It was the same one that took down Eric Cantor and John Boehner and that has bedeviled government for years. Call it establishment versus anti-establishment, or belief in governance versus political purity, or fidelity to ideology over party, or more simply: the beliefs of the Freedom Caucus.

Conservative Republicans were not any likelier than the average House Republican to oppose the AHCA. Although the bill was never brought to a vote, we can still get a pretty good idea of who opposed it using whip counts from news organizations. Specifically, we’ll look at the Republicans who voiced concerns about the bill or who said they would vote against it according to The New York Times and The Washington Post.

To gauge members’ left-right ideology, we’ll look at their first-dimension DW-Nominate scores. DW-Nominate rates politicians on a scale from negative 1 to positive 1 — negative scores are more liberal and positive scores are more conservative. There’s also a second dimension of DW-Nominate — we’ll get to that in a minute. Of the 210 current Republican members of the House who served in the last Congress and therefore have DW-Nominate scores, 48 registered as opposing or having concerns about the AHCA on at least one of the lists from the Times and the Post.

A slight majority of the would-be “no” votes came from House members who were more moderate than the average Republican. Indeed, it seemed in the final days that more and more of the no votes were coming from the more moderate wing of the party. There are 110 GOP representatives who rate as more conservative than the average Republican House member, and only 23 of them opposed the AHCA or expressed reservations about it.

Those conservatives who said they were against the AHCA, or at least had issues with it, had a key thing in common. Twenty of the 23 were in the lower right-hand quadrant. This quadrant represents more conservative members who also have negative scores on the second dimension of DW-Nominate. Congressional scholar Sean Theriault calls this dimension “partisan warfare,” suggesting that it identifies legislators who are more interested in scoring political points than in crafting policy. Negative scores seem to indicate members who are more anti-establishment and less willing to compromise. The second dimension helps define the Freedom Caucus. It’s visible on this updated version of a chart from 2015 showing how those who were part of the Freedom Caucus at the time lined up on the two dimensions of DW-Nominate scores.

Yes, the caucus is further to the right than other Republicans, but it also has mostly negative second-dimension scores. Put another way, for a lot of members a negative second-dimension score indicates a penchant for putting ideology over a functioning party. Many of the no votes for then-Speaker Boehner’s re-election to the speakership in 2015, for example, came from members with negative second-dimension scores.

Boehner was pushed out despite being slightly more conservative than the average House Republican. His problem was that the Freedom Caucus thought he compromised too much. Eventually, Boehner got fed up and resigned. After that, Majority Leader Kevin McCarthy folded his campaign to replace Boehner as speaker because he ran into issues mostly with members with negative second-dimension scores. McCarthy, of course, was only the majority leader because the previous majority leader, Eric Cantor, who had a positive second-dimension score, was defeated in a primary because he was too willing to compromise. Cantor’s replacement, David Brat, who has a negative second-dimension score, was a leading opponent of the AHCA.

Trump seemed to know that the Freedom Caucus would be a problem early on but didn’t appear to have learned from the past failures of Republican leaders. Yes, he met with Freedom Caucus members in the White House and called up members individually to try to get their votes. But Trump and Ryan were willing to make only so many policy concessions. As far as the Freedom Caucus was concerned, those concessions were not enough. Tim Alberta’s reporting for Politico reveals that Trump instead told them to vote for the AHCA for the good of the party. His phone calls to individual members relied mostly on charm and not on convincing them of the merits of the policy. He even seemed to threaten Freedom Caucus Chairman Mark Meadows’s re-election bid.

The political science literature suggests that Trump has little power to act on such threats. Although partisanship is strong in the current environment, parties are relatively weak. (See Boehner and McCarthy above.) Ryan and other legislative leaders have few means of punishing defectors or rewarding party loyalty. Members of Congress can raise their own money and communicate directly with constituents. Instead, what binds parties together is what political scientist Frances Lee describes as a team mentality. This loyalty to the team — and preference for keeping the other party out of power — drove many skeptical Republican members of Congress to support Trump during his presidential campaign. But now that the task is governing, with Republicans controlling Congress and the White House, the calculus has shifted. There isn’t a powerful natural opponent to fight. Furthermore, the unwillingness to compromise probably helps Freedom Caucus members with their Republican constituents. According to research from Matt Grossmann and David A. Hopkins, they are more likely to prefer ideological purity over pragmatic compromise.

The problem for Trump and Ryan now is that there is no way to placate the Freedom Caucus without upsetting more moderate Republican House members. The moderates may be more willing to compromise than the Freedom Caucus, but not if the Freedom Caucus members get everything they want. One remaining question is whether the caucus will start to function like a separate party that is only loosely affiliated with a major party, as the Southern Democrats did for much of the 20th century. Southern Democrats exacted lots of legislative compromises to protect their interests, most notably shaping public policy to preserve segregation and exclude African-Americans from federal programs. Since then, the specific issues and ideas have changed. Freedom Caucus members have a pretty good idea of what kinds of bills they don’t like. The question remains what kinds of concessions — if any — can bring them on board.