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.