In some places Democratic turnout seems stronger than anticipated. On Tuesday Minnesota had a special election to replace the late GOP Rep. Jim Hagedorn. Republican Brad Finstad won as expected, but by only four points. This is a rural district along the Iowa border, where Mr. Trump won by 10 points. Republicans also won a special House election in Nebraska this summer more narrowly than expected.

Part of this trend might be Democratic fervor to protect abortion rights after the Supreme Court’s decision overturning Roe v. Wade, similar to the voter surge in Kansas’s recent ballot initiative. If so, more might be in store. California, Kentucky, Montana and Vermont have abortion referendums scheduled for November. Republican candidates who could otherwise eke out victories might instead be swamped by Democratic turnout.

Democrats also want to keep Mr. Trump front and center in the campaign, as Monday’s FBI raid on Mar-a-Lago will do. That could backfire if GOP voters spy a case of unequal and retributive justice. But that will depend on what comes next and how Mr. Trump handles it.

The GOP should be making the midterms a referendum on Mr. Biden’s first two years. Democrats would prefer to talk until November—really, until the end of time—about Mr. Trump. Characteristically, so would Mr. Trump, and he has ensured GOP nominees who agree. The lesson of recent primaries is that this election is far from won, even in the House.