As Donald Trump continues his pundit-defying dominance of the national polls, with early primaries just days away, the once-unthinkable has become all too thinkable: Could Trump actually pull this off? Could he become president? I'm going to stake out a firm answer: no. Absent extreme and unlikely circumstances*, Trump will never be president. Jack Shafer argues that Trump's success so far is a "black swan" event, an unpredictable and unrepeatable concatenation of improbable circumstances. That sounds about right. But just because some political rules and conventions have been violated doesn't mean they've all vanished. Just because Trump makes no sense...