RealClearPolitics’ John McIntyre explains why today’s primary matters so much:
Barack Obama has had three previous opportunities to knock Hillary Clinton out of the race. First, in New Hampshire in early January where all the polls pointed to an Obama win; second, on Super Tuesday in early February where a win in California (where the polls were tied) would have been enough to cripple the Clinton campaign; and then most recently in Ohio and Texas in early March, where a popular vote win in either state would have been enough to effectively knock Clinton out of the race.
Senator Obama has another opportunity tomorrow in Pennsylvania - and this time he doesn’t even have to win. If he simply outperforms the latest RealClearPolitics Average which has him trailing by 5.9%, that will be enough to calm nervous superdelegates while all but eliminating any hope Senator Clinton has of claiming a popular vote victory.
Senator Clinton has a much higher hurdle. With time running out and Democrats increasingly anxious to turn their fire on John McCain, a win by 2-4 points along the lines of New Hampshire and Texas will simply not get the job done. Hillary Clinton needs a double-digit win.
And, here’s a quick guide to figuring out what tonight’s results might actually mean without all the spin:
–Obama wins: Race is totally over.
–Clinton wins by 5 or less: Race is effectively over.
–Clinton wins by 6-9: Status quo, which favors the front runner Obama, particularly as the clock winds down.
–Clinton wins by 10-13: Clinton remains the underdog, but her odds of being the nominee will be considerably higher than the conventional wisdom in the media.
–Clinton wins by 14+: Totally different race, as Clinton will be on a path to claim a popular vote win that will give her every bit as much of an argument as the legitimate “winner”. In this scenario anything could ultimately happen, including neither Clinton nor Obama becoming the eventual nominee.
By my guess, we’re likely to end up with something that’s a combination of scenarios two and three, but the political junkie in me would love to see scenario four play out.

