Around the time it was becoming socially acceptable for political scientists to accept that Donald Trump might win the Republican Party nomination for president, I wrote that perhaps the party had decided not to decide — that Trump offered useful cover for deeper and more intractable problems. While we are no longer living in those innocent times, I stand by two basic premises: Trump was a candidate who crashed the Republican Party, and the conditions within the party allowed that to happen.

People have different theories of what exactly happened during the 2016 nomination season, but I still think the most important causal factor was the party’s inability to coordinate. This problem also helps explain why the GOP is so focused and ideological, and yet still so divided.

I hypothesize that there are two basic problems. First, as I wrote last spring, no one has real leverage over anyone else. Second, the Republican Party places such a high value on ideological orthodoxy that it becomes a focal point of contestation for the nomination. This has a number of repercussions, but one of them is that it’s conducive to lots of candidates who claim to be the “true conservatives” or heirs to the Reagan legacy or whatever. And if the candidates and their supporters really care about and believe in ideological purity, it can be difficult to drop out and persuade supporters to go with someone else.

A few notes about the ideological purity hypothesis. It might help explain why Ted Cruz was ultimately Trump’s strongest rival. It’s harder to square with the fact that Trump himself ended up being the party’s coordination point. Maybe “if you obsess too much about purity, you end up with a total rogue outsider” is just a weird paradoxical outcome. Or maybe Trump satisfied some criteria that were important to people who cared about purity, even if many of his ideas early on were hardly Heritage Foundation–approved.

But Trump was the only coordination point Republicans could reach. He appealed to the “law and order” crowd, to the anti-immigration and “tough on terrorism” crowds, and enough to business and evangelical interests to win the nomination and then unify the party just well enough to pull off an Electoral College victory.

Now, it turns out that when you get elected, people expect you to govern. My friend and colleague Dave Hopkins has a good explanation of the role of resentment, suggesting it is a good basis for winning elections but a bad basis for governing. His argument is sound, but the foundations bear further scrutiny. Racial animus, anti-intellectual populism, and the violent project of protecting whiteness have long been part of American party politics. (Yeah, I talked about whiteness. Go ahead and tweet at me.) Some version of these elements defined the pre-1960s Democratic Party more often than not. What makes this version different?

Purity politics is even less conducive to governing than resentment politics. I hypothesize here, again, but as we think through the implications of what’s happening now, it seems important to know how to distinguish the two. They may amplify each other’s effects, or they may operate separately. But I don’t think they are the same thing.

Two additional coordination issues prevent the majority party from adopting policy. It really is stunning that a party with such relatively minor substantive policy differences has so much trouble coming together on a policy agenda. Not for the first time, I think there’s a good chance this comes down to a lack of mechanisms for coordination: distribution of resources, conventions that allow factions to work out their differences, leadership with real carrots and sticks. Furthermore, when congressional Republicans can find a political coordination point, which they managed to do in the House for the American Health Care Act, that point isn’t likely to create public policy that is broadly popular or solves the problems it aims to address.

It’s not surprising that congressional majorities might sometimes have trouble figuring out what the top priorities should be, or cobbling together a coalition from the individual interests of members of Congress, whose constituents may have vastly different interests when it comes to the details of policy. Congressional leadership and procedures can help!

In modern politics, presidents have also been part of the process of defining the legislative agenda that will offer something to different groups within the party coalition. This works better if you have a president who is well-versed and invested in public policy. (It can also help if the president is popular; it’s worth mentioning there’s some scholarly debate about the extent of the president’s power in this regard.) In other words, the same kinds of coordination problems that led to Trump’s nomination can also stymie the Republican policy agenda. But while Trump could save them in electoral politics, he’s not so likely to save them from their governing challenges.

What are the implications of this? First of all, this is really a set of theories about parties, and not specifically about the Trump presidency. But it highlights how closely the nature of the selection process is connected to the presidency itself, even though the discipline of political science treats these as separate topics.

Even though it’s tempting to think about this party challenge as mostly a procedural one, its deep substantive roots are important too. American politics will eventually reach a point where it has to address its racial issues, not simply swirl them into a mix of colorblind and coded appeals. That point is almost certainly past due.

Finally, I’d like to pick up on a point that Hopkins also raised his post: Are Democrats susceptible to similar problems? Purity politics hasn’t been as big a part of Democratic rhetoric. But dismantling the mechanisms of collective action is just as popular — maybe more popular — on the left.

The DNC has invited a lot of criticism, fair or not. Left-wing populism tends to aim at different targets than right-wing populism. But its basic tropes of empowering the people and demonizing powerful elites are similarly incompatible with the rules and compromises that make it possible to govern a large and complicated country. Candidates, parties, and factions that lose sight of this goal are taking a big and serious risk.