What Should Worry Democrats on Path to Midterms

Almost six months into President Biden’s first year, some yellow warning lights are flashing for Democrats.

The president’s party has plenty to feel good about, to be sure. The economy’s recovery from the coronavirus slide is proceeding apace, and the stock market, which former President Donald Trump predicted would collapse upon his departure, actually is up 10% since the Biden inaugural. Mr. Biden’s approval ratings are solid, and the infrastructure deal struck last week with Senate Republicans has the potential to become a long-sought bipartisan achievement.

Yet Democrats control Congress by the narrowest of margins, and face a...