The Squad may end up adding another member in November. Supporting Medicare for All and being the son of the founder of the Congressional Black Caucus wasn’t progressive enough for longtime incumbent William Lacy Clay to hold into his House seat in yesterday’s primaries. Clay went down to defeat in his primary challenge yesterday from Black Lives Matter activist Cori Bush:

Clay, 64, is the third Democrat this cycle to lose his seat to a challenger more plugged in with the party’s most progressive wing.

Clay’s defeat stands out because he is Black and focused on civil rights issues throughout his ten terms in Congress. His father, William L. Clay, was a co-founder of the Congressional Black Caucus.

Both candidates supported progressive causes like the Green New Deal and “Medicare for All.” But Bush argued that it was time for a change and criticized Clay for taking campaign contributions from political action committees and corporations.

Those points resonated in the majority-Black 1st District, where a national reckoning on police relations with Black people was sparked by the 2014 protests over the fatal shooting of Michael Brown in Ferguson, Clay’s hometown.

The surprise isn’t so much that Clay lost, but that Clay got challenged in the first place. Clay sounds like an almost perfect Bernie Sanders acolyte. Why did progressives bother to challenge him at all? Alexandria Ocasio-Cortez’ challenge to Joe Crowley at least made some ideological sense, but all this does is pick off one of the leading African-American members of the House for not much change at all — except to reduce the influence of the district’s voters:

Mr. Clay, the scion of a storied Black Missouri political dynasty in his 10th term in Congress, had tried to make the campaign a referendum on not only Ms. Bush’s suitability for elected office but also the progressive movement behind her. He carried out a series of dark, personal attacks in the campaign’s final days to try to halt Ms. Bush’s momentum and described her as a “prop” of out-of-town interests seeking to divide the Democratic Party along racial lines.

Mr. Clay highlighted his own ties to the Democratic power structure, earning endorsements from Speaker Nancy Pelosi, Senator Kamala Harris of California and groups like Planned Parenthood.

These days, that kind of resumé doesn’t get you far, not even in a D+29 district. Combine that with Clay’s support of the progressive agenda, and it starts becoming clear that progressive activists aren’t making these primary-challenge decisions based on ideology as much as their ability to gain power.  In that sense, Justice Democrats — the same group that vaulted AOC into office — can ring up an easy win. They took a victory lap last night:

Late Tuesday night, it was Justice Democrats, which helped groom Ms. Bush and other successful progressive challengers, that was celebrating.

“If you don’t know, now you know: The Squad is here to stay, and it’s growing,” said Alexandra Rojas, the group’s executive director.

It doesn’t look like it’s shrinking, at least so far. Rashida Tlaib has a 2:1 lead over Brenda Jones in early vote counting in Michigan, although it’s far too early yet to call that race, thanks to a massive amount of mail-in ballots. Ilhan Omar faces voters in MN-05 next week, and it looks like Ayanna Pressley is running alone in Massachusetts’ September 1 primary. But even if The Squad grew by one this time, it did so by essentially eating its own. That’s many things, but it’s hardly progress, and it’s likely to make other House Democrats even less happy with Justice Democrats and AOC.