For the last 80 years, America has been a leading advocate of free trade. It built (and benefited from) the rules of the global economic system. But as the Trump administration imposes record tariffs on allies and renegotiates trade agreements around the world, it’s no longer playing by the rules it created. Instead, it's becoming the most protectionist advanced industrial economy in the world. What happens when globalization's biggest backer becomes its biggest critic?