Some have urged that Omar’s “some people did something” words about 9/11 be understood in context. Let’s try that. After the Christchurch massacre in New Zealand, Trump tweeted: “My warmest sympathy and best wishes goes out to the people of New Zealand after the horrible massacre in the Mosques. 49 innocent people have so senselessly died, with so many more seriously injured. The U.S. stands by New Zealand for anything we can do. God bless all!” By using died rather than were murdered—and by describing the crime as “senseless”—Trump abstracted a politically motivated act from the politics that motivated it. The crime became a ghastly tragedy, requiring no words from him about the white-nationalist beliefs of the killer or the larger international movement that shared those beliefs.

“Some people did something” performed exactly the same exonerating service for Islamic extremism as Trump’s tweet about Christchurch did for white nationalism. Like Christchurch in Trump’s telling, in Omar’s telling, 9/11 just … happened. Look no further. Do not ask about the ideas that impelled the crime. Do not criticize those ideas. Do not hold to account those who traffic in dehumanizing language like that used by Omar’s co-headliner in California.

Omar, in her turn, has been a target of extremist criticism, some of it verging on incitement. She should be free to express her thoughts about Jews, about 9/11, about her distrust of the democratic opposition in Venezuela without fear of harm. But now the combined operations of Trump and the ultra-progressive edge of American politics have put them beyond normal political criticism within the Democratic Party, sticking her co-partisans with responsibility for whatever outlandish remark next tumbles from her lips.