Mr. Obama and his advisers, Council on Foreign Relations president Richard Hass wrote this week in the Financial Times, “tend to exaggerate the costs and risks of acting and discount those of inaction.” That allows threats to grow, eventually requiring a more costly response.

This is where Mr. Obama finds himself now. His administration is desperate to avoid mission creep in Iraq. But that’s exactly what’s happening. “We’re not going to let them create some caliphate through Syria and Iraq,” the President told The New York Times last week.

Almost 1,000 U.S. military personnel are back in Iraq. And after insisting there would be no U.S. troops on the ground, the Pentagon is reportedly hatching plans for boots on the ground.

Mr. Obama is learning the hard way that, sometimes, it’s stupider to do nothing.