This could well be the first election since 2000 with an independent candidate. That has happened only four times in the past century, the others being 1912, 1948 and 2000. And a three-way -- or even a four-way race --would be a wild card. It could take any of several forms, with different partisan winners and losers. Consider: Suppose Donald Trump is the Republican nominee and Hillary Clinton is the Democrat. Establishment Republicans will be convinced that their party has been hijacked by a bizarre rabble-rouser; GOP elites will be unsure which is worse -- the prospect of Trump losing, or Trump winning. Result: pressure builds for a "real" Republican to run as an independent -- a conservative but not a rightwing populist. That could be, say, Paul Ryan, or John Kasich, or Mitt Romney again. Advantage: Democrats.