WASHINGTON, June 14 -- Donald Trump campaigned on a single, simple promise that voters could feel at the gas pump and the grocery checkout: he would bring prices down. In May, they went the other way, and hard. Consumer prices rose 4.2 percent from a year earlier, the Labor Department reported, the fastest annual inflation in more than three years and a jump from 3.8 percent the month before. The two forces driving the increase are not abstractions of the global economy. They are the president's own policies: the war he launched against Iran, which has sent energy prices soaring, and the tariffs he has imposed on nearly everything the country imports.

The headline number, released June 10, was bad enough on its own. As CNBC reported, pri...