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. Continued...