Donald Trump, of all people, must be familiar with the adage that a good salesman knows when to stop, and he is nothing if not a good salesman, especially when the product is himself, because he's so convinced of its excellence. For a while it was easy to dismiss him as an aberration, a political sideshow in the grand and glorious tradition of such notable gadflies as Ron Paul or Ross Perot or Ralph Nader or Lyndon LaRouche, all of whom were generally regarded as nuisances, taking up valuable time and space better spent on candidates who were seen as actually having a chance to win.