One possibility, Weaver said, is that the left will become “much less thoughtful in the future about which incumbents get challenged.”

Or in some places, progressives could even forgo primaries, altogether, running general-election candidates as independents in swing districts. They might not win, but they could split the vote just enough to prevent a centrist Democrat from coming out ahead of the Republican.

“Can they get 5 to 10 percent of the vote in some swing districts?” Weaver asked. “I think they can … That is certainly an option.”