It depends what you mean by "win"
John McCain is hoping to sew the nomination up, and seems increasingly likely to do it. The Republicans rely on "winner takes all" for translating primary votes into delegates. This ought to speed the process. The polls show no sign yet of a Romney recovery.
The Democratic race is different, of course. It looks extremely close, and the party's rules apportion delegates using a formula that rewards votes cast, district by district, regardless of who wins the state-wide vote. The likely question for the Democrats is not who "wins"--barring an astonishing upset, neither Hillary Clinton nor Barack Obama will triumph outright--but which of them leads going into the final lap. If Barack Obama emerges tomorrow even neck and neck with Hillary, that is a victory of sorts in itself. And the odds would tilt his way going forward, since the schedule for the remaining primaries levels out. The more time he spends with voters, the more they seem to like him: the Super Tuesday frenzy worked to his disadvantage. And money to support another spell of hard-fought campaigning for the nomination is not a problem for him: the cash continues to pour in.
In the past two or three days, many commentators have been extrapolating Obama's recent strong surge and, though mostly not daring to say it in print, guessing he would win big today. It could still happen--though Gallup's tracking poll suggests that Obama's national momentum might have peaked just too soon. Then again, it's votes in the states that count, and the state polls have been very unreliable up to now. California, for instance, is a crucial battle: one new poll there puts Obama well ahead; another says Clinton is leading.
The waiting is the hardest part...