And the outcome? Hillary probably still wins. The history of Democratic primaries has always been that challengers emerge and run stronger than anyone believed they would but then fade and the front-runner prevails after all (see Bradley in 2000, Tsongas after New Hampshire and Brown after Connecticut in 1992, Gore after the Southern primaries in 1988, Hart in 1984 and Kennedy in 1980).
And among the Republicans? Who knows? The race would be thrown into chaos. Anyone could win. Romney would have the momentum, but doubts about his ability to win as a Mormon would make his lead unstable. Huckabee would be gaining, but he may not be well enough known to make it. Giuliani could still recover, given his strong national standing, but would be hobbled. And McCain would still have his immigration position hanging over his head, but as Rudy falters, he might pick up the slack.
Then again, Hillary could open up a large lead in Iowa as her juggernaut gets going. And Rudy could, at least, finish a strong second to Romney in Iowa, and perhaps beat him, making it a Giuliani-Romney runoff in the main primaries, which Rudy probably wins. Then the general election match-up would be Hillary vs. Rudy, as we have all anticipated.
But what if?