The Gordian Knot that Donald Trump has tied around the Republican Party tightened considerably when the presidential frontrunner issued his call for a ban on Muslims entering the United States.

If there was any doubt, that bind became clear within the span of about 10 minutes during a press conference Speaker Paul Ryan held on Tuesday morning with the House Republican leadership in the Capitol. As the GOP’s top elected official in Washington, Ryan has pledged to stay publicly neutral in the party’s primary race. He ended his introductory remarks, however, with a strong denunciation of Trump’s proposal—delivered entirely without uttering the candidate’s name.

“Normally, I do not comment on what’s going on in the presidential election,” Ryan began. “I will take an exception today.”

This is not conservatism. What was proposed yesterday is not what this party stands for, and more importantly, it’s not what this country stands for. Not only are there many Muslims serving in our armed forces, dying for this country, there are Muslims serving right here in the House, working everyday to uphold and to defend the Constitution.

Some of our best and biggest allies in this struggle and fight against radical Islamic terror are Muslims—the vast, vast, vast majority of whom are peaceful, who believe in pluralism, freedom, democracy, individual rights. I told our members this morning to always strive to live up to our highest ideals, those principles in the Constitution on which we swear every two years that we will defend.

Ryan also reminded reporters that when the House voted last month to suspend the Syrian refugee program, he made clear that there should be a security test—not “a religious test”—on people entering the U.S. Freedom of religion, he said, was a “founding constitutional principles.” His aides let it be known that Ryan had told Republican lawmakers in private that Trump’s proposal violated two different amendments in the Bill of Rights: the First and the Fourteenth.

Yet when it came time for questions, Ryan retreated to boilerplate. A reporter asked the obvious: Would Ryan support Trump if he became the Republican nominee for president?

“I’m going to support whoever the Republican nominee is,” the speaker replied, “and I’m going to stand up for what I believe in as I do that.”

In other words, Ryan may believe that Donald Trump is proposing a policy that would violate the Constitution and his oath of office, and would amount to an impeachable offense if he put it into effect, but he’d still support him over (presumably) Hillary Clinton if it came to it. As political logic goes, that’s pretty close to an untenable position, and it’s one that Trump is increasingly forcing both the party establishment and his rivals for the nomination to confront. If he’s so bad, how could you in good conscience support him?

My colleague Peter Beinart noted even before Trump’s outlandish call to ban Muslim entry to the U.S. that Republican candidates like Jeb Bush and John Kasich had struggled to answer the same question. Kasich, in particular, has criticized Trump with as much passion as anyone; his supporters have compared him to Hitler, and in response to his proposal yesterday, Kasich said he was “entirely unsuited” to be president. Bush tweeted that Trump was “unhinged.” If he is so bad—unhinged and dangerous—how could you in good conscience support him? The candidates have mostly dodged the question by predicting that Trump won’t win, but the longer he stays atop the polls, the weaker that answer will become. It will likely be a key part of next week’s GOP debate.

Trump’s trump card, of course, is the possibility that he’ll run as a third-party candidate if the GOP treats him unfairly. And in that sense, he’s holding the party hostage. For now, he seems to control a bloc of voters the Republicans need to defeat Clinton, and an independent run could mean a nightmarish repeat of the election of the first President Clinton in 1992, in which another billionaire—Ross Perot—siphoned support and helped Bill win the presidency despite capturing just 43 percent of the popular vote.

For now, Ryan and his colleagues are still trying to counter Trump without pushing him away entirely. But as he dabbles in ever-darker areas of American politics, the tightrope they’re trying to walk may disappear entirely.