Unreliable

 The root of American power since World War II has been our more-or-less dependable nature. Sure, individual president's altered the focus of American foreign policy, but there were some agreed upon ideas that carried over from one administration to the next.

Trump's decision to blow up the North American Free Trade zone is bad on multiple layers. It should lead to massive supply line issues. It should lead to higher prices. But, as Krugman points out, it will destroy the idea of an America that even pretends to honor their agreements. A hegemonic power that agreed to bind itself with treaties was a historical rarity, and now that special situation is leveled by the worst person to ever defile the Oval Office.