Donald Trump wins again. Oh, he's still not going to be president. His new offensive — coming out for a "total and complete shutdown" of Muslim immigration and travel to the U.S. — won't get him any closer to taking over the White House. But he has once again succeeded in taking over the news cycle.

Attention that could have gone to whether U.S. President Barack Obama's strategy to destroy Islamic State has any chance of success is instead going to Trump's latest half-baked idea. Actually, that gives it credit for too much time in the oven. Trump's plan would work on the honor system, apparently: We'd ask travelers if they're Muslim and turn away those who say yes.

But as unserious as the proposal is, it's worth thinking through what's wrong with it, if only to clarify the continued relevance of our tradition of religious tolerance in the age of terrorism.