That creaking noise you hear is the sound of me going way out on a limb to predict that Barack Obama will win the Pennsylvania primary on Tuesday, finally ending Hillary Clinton's presidential ambitions.

After all the sound and fury, the race in Pennsylvania will come down to the strength of get- out-the-vote (GOTV) operations, and I think the Obama campaign's organizational advantages will be enough to push Obama past Clinton by almost two percentage points. He's got money, he's got energy and enthusiasm (despite his debate performance on Tuesday), and he's got Philadelphia and its suburbs

Broadly speaking, presidential elections are almost always decided by what and who Americans think best suit the moment. After all the wins and losses, after all the gaffes, the deceptions, and the rare moments of inspiration, Obama is simply closer to the mood of the country than either Clinton or McCain.

Obama is selling change. Both of his opponents are selling the virtues of experience, but voters, fed up with the way things have been going, view experience as more of a problem than a solution.

Still, it's an election and Obama can blow it (he erred in, among other things, not anticipating the controversy over the Rev. Wright ), but he has shown himself capable under attack, and in Pennsylvania he has some underreported advantages.

At first glance, Pennsylvania, one of the whitest, oldest, and most working-class states in the country, should be Clinton's to lose. The demographic numbers are indisputable, but the beating heart of Democratic politics in the Keystone state is Philadelphia -- and now, its suburbs -- and the whole region is indisputably in the Obama column.

Since Election Day 2007, 306,686 people have registered as Democrats in Pennsylvania -- more than 45 percent of them (139,000) in Philadelphia and the Philly 'burbs. And two college counties, Centre, 19.6 percent (Penn State), and Union, 17.3 percent (Bucknell University), are in the top three counties in terms of the percentage increase of new Democratic voters. Again, it's fair to assume most new registrants are Obama voters. He will not win northeast Philadelphia or some precincts in south and southwest Philly, but he will still win by a large margin in the Philadelphia region.

The path to an Obama win is relatively straight forward: Run up the numbers in and around Philadelphia, fight for and maybe even win the Lehigh Valley cities Bethlehem and Allentown, and minimize his losses in the west. This is a strategy that tracks with Democratic victories in Pennsylvania in recent years.

Here, finally, is why I think he wins:

• Clinton hasn't succeeded in making any of her criticisms of Obama stick. He has managed to weather scandals that would sink a politician of lesser skill.

• Clinton has been most effective when she is seen as the victim and underdog, but, given her aggressive response to Obama's "bitter" comments and her established strength in Pennsylvania, neither of these circumstances apply. If he can resist the urge to complain about his treatment in the debate, he may be the one seen as a victim.

• Bob Casey Jr.

The importance of Casey's endorsement of Obama is hard to overstate. In part that's because Pennsylvania's junior senator is as daring as a piece of Lackawanna anthracite coal and is seen as unwilling or unable to play cynical political games. What's more, he is an able counterbalance to Clinton's two biggest supporters -- the affably pugnacious Gov. Ed. Rendell, and Philadelphia's African American mayor, Michael Nutter.

Casey is also exactly the kind of conservative, Catholic, blue-collar Democrat that Obama is supposed to have the most trouble attracting. He needs Casey's help all the more now that some of these voters think that he sees them as clinging to guns and religion out of a sense of economic frustration. In a new ad for Obama, Casey makes the election clearly about the economy, declaring on camera that "in towns like yours and mine, families are struggling with bills they can't afford and jobs moving away. It has to change -- but it won't until we change Washington."

But Casey's endorsement does something less obvious for Obama -- it rescues him from being the "Philadelphia candidate" and all the taint of racialized politics, corruption, and urban decay that such a label would put on him. This is especially true when Casey's support is contrasted with Rendell's and Nutter's, since both are current or former mayors of Philadelphia.

So my call is Obama by a point and a half. Creak ...