Ever since the world economy began spiraling into recession last fall, economists with a sense of history have warned against the protectionist reflex. It was cascading trade barriers that deepened and prolonged the Great Depression. Last weekend, at their annual meeting in Whistler, B.C., Canadian mayors—frustrated over U.S. “By American” rules—voted to block U.S. bidders from getting a slice of stimulus infrastructure spending in Canada. Now, as this story reports, the Canadian government is launching a full-court lobbying press to try to persuade the U.S. Congress to drop the protectionist procurement policies that started the spat. Despite all the warnings, tit-for-tat protectionism seems now to be a serious threat.