Salena Zito

Welcome to Pennsylvania. Check your assumptions at the door and take nothing for granted -- because this commonwealth is about to become the epicenter of the political universe.

“The Democrats can't win the presidency without Pennsylvania's electoral votes,” says Charles Franklin, professor of political science at the University of Wisconsin-Madison.

Steve McMahon, an analyst for the Democrats, says that is why Barack Obama’s campaign showcased three Pennsylvania favorite sons at its convention. “The fact that all three, Sen. Bob Casey, Rep. Patrick Murphy and Scranton native Joe Biden, are white Catholics with working-class backgrounds” -- a tepid Obama demographic -- “indicates just how important that vote is in Pennsylvania,” McMahon explains.

And “McCain knows, too,” says his former top adviser, John Weaver. Weaver thinks the presidential race will be won on a straight line between Lansing, Mich., and Philadelphia -- if McCain can swipe either Michigan or Pennsylvania from the Democrat column.

Obama and McCain already are working on wooing Western Pennsylvanians. On Friday evening, less than a day after his acceptance speech, Obama and Joe Biden were scheduled to make Beaver County's Irvine Park the first stop on their three-day bus tour. And on Saturday McCain was scheduled to appear in Washington, Pa., with his surprise VP pick, Alaska Gov. Sarah Palin -- a pro-life hunter, fisherwoman and hockey mom with a son heading off to Iraq who is tailor-made for many voters in every corner of Pennsylvania.

The appearances of Obama and McCain reinforce the importance to each of their campaigns of winning over Pennsylvanians, who are not monolithic by any means and in many ways have beliefs and values that run counter to their national parties. Let’s take a quick regional tour of the state's voters:

The Northwest -- Some Republicans, but a larger number of socially conservative, pro-life, pro-gun, Catholic-labor Democrats. Their economy is hurting due to the loss of manufacturing jobs and they want answers -- not “bitter” attacks.

The Southwest -- Home to the same kind of Democrats, except that they run the show at the local levels. In terms of identity and race, they have little in common with Obama, the law-school professor; they have more in common with prisoner-of-war hero McCain.

They want answers to their economic concerns. But they have lived through harder economic times -- so they don’t want more taxes. They want oil drilling and they do not want House Speaker Nancy Pelosi stepping on their Catholic beliefs about abortion or Obama and running-mate Biden grabbing their guns.

McCain probably will win Butler and Westmoreland counties. And while the GOP brand is tarnished nationally, the Democrat brand is hurting due to the state Legislature’s “Bonusgate” scandals. McCain could win five other counties: Cambria, Beaver, Washington, Greene, Fayette; Obama is just too much for their voters to take.

That leaves Pittsburgh and Allegheny County: The winner of these wins the state -- and likely the presidency. They’re up for grabs, and neither Casey nor Pennsylvania Gov. Ed Rendell can help Obama here, though former Gov. Tom Ridge can, and will, be able to help McCain. McCain has the edge here due to social issues, veterans, seniors and an ability to cut into the Jewish vote.

The Northeast -- More socially conservative Democrats, but Casey and Biden (who was born in Scranton) should provide hometown pride for Democrats to seize this region for Obama.

The Center -- A few urban pockets (including more progressive Dauphin County, home to the state capital), but these counties are bedrock GOP country. McCain may not be Bush and is not beloved, but for these counties, Obama is a liberal from way beyond their world. Agriculture, guns and God all play huge here, so McCain sweeps.

The Lehigh Valley -- This will be a battleground. Obama needs to win here (and can) but needs to campaign hard; McCain has a small chance to eke out a win but more than likely will lose Northampton County, where an emerging Hispanic populace could be a decisive factor.

Philadelphia’s “collars” -- In Philly, black voters will provide a sweep for Obama. Philly’s four suburban collar counties also should go for Obama -- but McCain can appeal to a large Jewish populace on Israel, on his strong military background and on his maverick views.  Bucks and Delaware counties have large Catholic populations that Biden (who shares their Philadelphia media market) can influence. Run right, the McCain campaign can win Chester and Bucks counties but probably will lose Montgomery.

“Pennsylvania is a must-win for the Democrats,” Purdue professor Bert Rockman insists. “If the Republicans win it, then it is likely that Ohio will also fall their way, too, and very likely Indiana as well.

“So, as Pennsylvania goes …” Rockman says, his voice trailing off into an unspoken conclusion: so goes the nation -- and the presidency.

Salena Zito

Salena Zito is a political analyst, reporter and columnist.