Rich Lowry: Enforcement, not separation, is the issue

President Donald Trump climbed down on separating families at the border, but the underlying argument is not going away.The central question isn’t whether we should separate families — even most immigration hawks would prefer to hold families together — but whether migrants should stay in the United States or not.Trump hopes to salvage his “zero tolerance” policy by holding parents and children together, although the practical and legal obstacles will be formidable.