Of all the proposals made by the Trump administration since the start of the year, this will be the most damaging in real terms. To "rip up" NAFTA by comparison might take years to show its effects, while tossing the "Dreamers" out of the country will drive them underground and make criminals out of 800,000 people. Business leaders in the U.S. oppose such a move. The G.O.P. is being split on the issue (again).