We’re still waiting for the final results of the 2022 election. But it’s clear that Democrats decisively beat both expectations and the elections’s “fundamentals”—the incumbent party’s usual midterm losses, President Biden’s low approval rating, high inflation, voter negativity on the economy and the state of the country. Republicans look set to take back the House but only by a modest margin. And the Senate will remain in Democratic hands, albeit narrowly. The Democrats’ relatively good night is attributable, above all, to their secret weapon: Donald Trump. Mr. Trump’s ability to push Republican voters into picking bad, frequently incompetent candidates with...