President Obama claimed credit at a Los Angeles fundraiser last week for “the steady progress that happens when people who love this country decide to change it,” and reality is unlikely to darken his farewell tour. But for everyone else, note that the largest U.S. health insurer is quitting ObamaCare.

On Tuesday UnitedHealth Group reported a terrific first quarter, with strong performance across nearly all business lines. There was one exception: The conglomerate’s insurance exchange unit raised its projected Affordable Care...