If politics is the art of the possible, what’s possible changed dramatically on Tuesday.

In recent weeks, it was possible to imagine the Republican Party’s nomination going to someone other than the remaining candidates: Donald Trump, Ted Cruz and John Kasich. In the final tally, none may have enough delegates to meet the party’s threshold for winning the nomination on the first ballot. For this reason, speculation in Washington has been that House Speaker Paul Ryan might step in.

Earlier this week, Ryan narrowed the frame of what’s possible. Twice.

“I do not want nor will I accept the nomination for our party,” he said.

Then, in taking himself out of consideration, he did something else. He suggested that anyone other than Trump, Cruz and Kasich is out of bounds. He said: “I believe [delegates] should only choose from a person who has actually participated in the primary. … If you want to be the nominee, you should actually run for it.”

This casts doubt on efforts to draft Mitt Romney, the 2012 nominee, or anyone else. The press has reported on efforts to conscript military generals and other notables. If the party was in a pickle before, it’s more so now. Who to choose?

First, Kasich. The Ohio governor has no chance of coming close to the 1,237 delegates needed to win. His aim now is to present himself as a compassionate alternative to Trump and Cruz, perform modestly well on the coasts, where Republicans are more moderate, and ride the horse all the way to the convention.

Kasich is in fact much more conservative than Trump. That should give heart to the Christian right and business Republicans. He’s only nominally less conservative than Cruz, but he expanded Medicare in Ohio under the Affordable Care Act, which is beyond the pale to the Tea Party faithful. Kasich’s biggest challenge as the “fourth place candidate” is his dearth of delegates. Choosing Kasich wouldn’t be much different in terms of its anti-democratic impression than choosing Paul Ryan.

Second, Cruz. He is positioning himself as the conservative alternative to Trump. He won’t have the same delegate obstacles as Kasich. Indeed, Cruz has mounted an impressive strategy to manipulate party rules in states like Colorado and Utah to fight for every delegate. Trump hits home runs, but Cruz plays small ball to win.

The main issues facing Cruz are twofold. One is that despite winning Wisconsin, and calling it a turning point in the race, he still can’t get power brokers to unify around him. Yes, GOP donors and Congressional leaders desire an anti-Trump, but in not embracing Cruz wholeheartedly, they are showing worrying signs of ambivalence. His other problem is about 40 percent of the GOP electorate isn’t conservative in terms of the appropriate role of the federal government in the lives of Americans.

We can thank Trump for that. He has shown that even Republicans like many things progressives have fought for, including social insurance programs, fair-trade deals, infrastructure investment, and clean energy. Indeed one of Cruz’s proposals, eliminating whole segments of the federal government in the form of the Departments of Education, Commerce, Energy, and Housing and Urban Development, is favored by just 18 percent of voters, according to a Gallup poll.

Finally, Trump. Yes, Trump.

Say what you will, but the celebrity billionaire has the majority of delegates now and likely will have by July’s convention. If the party denies him the nomination, it will feed into the already entrenched view that the GOP elites don’t care about the base, in which case Trump supporters will have three choices: vote for the nominee, vote for a Democrat or stay home. Given that Trump voters are the most disengaged voters, according to survey by the Public Religion Research Institute, I’m guessing the Republicans can expect to kiss a huge bloc of voters goodbye.

To be sure, Trump is a flawed candidate. His favorability ratings are the lowest of all the candidates, Democrats included. But that may partly be the result of party infighting. It’s reasonable to suggest that his favorability will climb as the party consolidates around Trump, pushing him to the finish. Yes, with Trump as the nominee, the odds are against the Republicans in winning the general election.

But without party unity, it’s close to impossible.

John Stoehr is a lecturer in political science at Yale and the 2016 Koeppel Journalism Fellow at Wesleyan.