To understand the rise of Donald Trump, you’d do well not to fixate on the fact that he’s running under the Republican banner. During Thursday night’s Fox News debate, Trump made it clear that failing to secure the GOP nomination wouldn’t stop him from exploring an independent candidacy. And honestly, he’d be crazy not to. Trump is very far from a Republican regular. He represents an entirely different phenomenon, one that bears little resemblance to garden-variety American conservatism. That’s why Republicans shouldn’t fool themselves into believing that one lackluster debate performance will send him packing. Go to almost any European...