This week, Daniel Howes says President Donald Trump’s whipsawing on trade and tariffs is exhausting the very people it’s intended to help. Threats to close the U.S.-Mexico border are withdrawn … only to be replaced by the promise of new tariffs on cars, trucks and SUVs built in Mexico for the U.S. market. This is what "Art of the Deal" leverage looks like. It’s a blunderbuss of scattershot intimidation whose practical effect would be to impose acute economic pain on the industrial Midwest – the very region whose voters delivered Trump to the White House.