What happened Saturday in American politics was profound, and for Donald Trump, it marks the likely death of his presidential campaign. The permission structure that was slowly, reluctantly built around Trump by the media, by the Republican Party, by the conservative movement, and by Trump himself, is crumbling, and there is no time to rebuild it before the election.

Since Trump won the GOP primary, his party has been working to normalize an abnormal, unpopular, and frankly bizarre candidate. Trump has always had the support of his hardcore fans — but he needed more than that. He needed the mainstream Republicans who didn’t vote in the GOP primaries, or voted for someone else; he needed the independents who didn’t like Clinton, but didn’t trust Trump; he needed the movement conservatives who had entered politics to ban abortion and shrink the government, and who saw little of their crusade reflected in Trump’s history.

Trump needed, to put it simply, the support of a lot of voters who didn’t like him.

The effect of all this has been to build a floor under Trump’s vote share, and his media coverage. He might lose the election, but so long as Republicans were able to signal that he’s the guy you vote for if you don’t want Hillary Clinton, he couldn’t lose it that badly — and a three-or-four point loss would probably mean Republicans kept the House and Senate. By the same token, Trump gets plenty of bad press, but so long as the Republican Party stood behind him, he had to be covered as a basically normal candidate, not as a dangerous virus that had somehow infected American politics.

And now that’s crumbling. The wave of Republican defections from Trump’s side is the same process that normalized him, but in reverse. Just as Republicans felt more and more pressure to support his candidacy as other Republicans signed on, Republicans — and everyone else — will feel more and more pressure to abandon his candidacy as their co-partisans defect.

Two weeks ago, supporting Trump was what you did if you were a Republican. Today, abandoning Trump is what you do if you’re a decent person. Two weeks ago, Trump’s floor was probably the mid-40s. Now it is plausibly much lower — I would no longer be surprised to see Trump’s vote share dip down into the 30s, with disastrous results for the Republicans congressional majority.

Trump is becoming de-normalized, and the structure that made it safe for Trump-skeptics to vote for him is crumbling. That is a very dangerous dynamic for the Republican nominee, and for the political party that tried for so long to protect him.