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As regular Slatest readers know, we usually spend this newsletter answering questions about the news. Sometimes, though, it’s worth taking the time to pose big questions we don’t currently have answers to. So after yet another bitter primary election this week that pitted Democrats’ progressive and moderate wings against each other, let’s explore one crucial question that confronts the party going forward: Will all these rancorous nominating contests hurt Democrats’ chances against Republicans in November?

Healing those wounds is no small challenge. Democratic divisions have been front and center this year. (Losing another presidential election to Donald Trump will do that to a party.) Some of the divides are over ideology and policy; in last week’s Michigan Senate primary, Abdul El-Sayed, a progressive supporter of Medicare for All, narrowly beat Rep. Haley Stevens, a pro-Israel centrist. Others—including Tuesday’s Wisconsin governor primary, in which the moderate David Crowley even more narrowly defeated Francesca Hong, a democratic socialist—are about which candidate is better equipped against Republicans or is advocating exciting new ideas.

Divisive primaries happen for a reason; they can help parties work out policy disagreements or stress-test candidates’ mettle. But bridging those divides isn’t easy, and this year’s primary season could haunt Democrats in key races this fall. Political science research suggests that longer and more competitive primaries can ultimately cost the party’s nominee votes in the general election. Only one candidate can win, after all, which leaves plenty of room for hurt feelings among the losing contender’s supporters—some of whom might choose to stay home rather than vote for someone who wasn’t their first choice.

Several of this year’s bitterest primaries so far also involved more than two candidates; this can split the vote such that no one gets a majority. That’s what happened in Michigan (where........

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