So he wants the four congresswomen front and center, which is where his tweet put them. They put themselves there on Monday, at a news conference to respond to him. Omar called for his impeachment. I bet he was fine with that.

The four congresswomen — the Squad, as they’ve come to be known — make the Democratic Party look much more progressive than it actually is. The president and his minions are counting on that. And unlike Democrats’ eventual pick to take on Trump, the Squad won’t be sanding down their most leftward edges or striking notes ambiguous or elastic enough to soothe the center. That’s a presidential-nominee thing. That’s most definitely not a first-term-in-the-House thing.

These four are also a tool for promoting discord in the Democratic ranks, because as the recent feud between them and House Speaker Nancy Pelosi demonstrated, plenty of their fellow Democrats find them too fantastically idealistic, too censorious of those who disagree with them, too quick to play the race card, too much.

For now, Trump’s shocking and unconscionable tweet has downgraded that feud and united Democrats, who immediately drafted a House resolution that formally condemns his comments as racist. They’re daring Republicans to vote against it and seemingly go on record in support of what he said. But that’s just for now. What happens next week, next month and next year is an open question.

It’s no accident that around the same time that Trump fired off his racist tweet, Democratic strategists were, according to a report in Axios, circulating a private poll of potential swing voters — white people with two years of college or less — that showed that 74 percent of them recognized Ocasio-Cortez’s name but only 22 percent had a favorable view of her, while 53 percent recognized Omar but only 9 percent saw her favorably. If Democrats have numbers like that, Republicans almost certainly do, too. And Republicans know how to pick — and pick apart — their enemies.

But Trump is up to something else as well. He means to send liberals into such a fury that they believe that passionately calling him out and urging the opposite of whatever he’s saying and doing are strategy enough. He’s baiting them.

Why are so many Democratic presidential candidates recommending what sounds a lot like open borders, which won’t go down well with many of the voters the party needs? It’s a response in part to Trump’s xenophobia and cruelty when it comes to immigration.