In 2010, Pennsylvania will have hot races for governor and the U.S. Senate, too. Add the seat left by Republican U.S. Rep. Jim Gerlach in the Southeast – a close race that will have tons of money from both parties – and you have Pennsylvania once again at the epicenter of national politics.

Right now, the state’s biggest buzz is the “Joe-mentum” radiating from the declared but unfiled U.S. Senate candidacy of Rep. Joe Sestak, a Delaware County Democrat who is taking on the 28-year incumbent and newly-declared Democrat, Arlen Specter.

When Specter switched parties this spring, he bargained for (and got) the field cleared by President Barack Obama and Gov. Ed Rendell, first with their endorsements and then with their mandates that party members follow suit.

What they did not count on was the tenacity, persistence and appeal of Sestak, who refused to clear a path for Specter, or the tepid response from committee members and party chairs to the long-time Republican Specter.

“Leadership can only make endorsements, and while it is good to know where they stand, that does not mean we have to fall in line,” says Jim Burn, the Democrats’ Allegheny County chairman.

Villanova University’s Lara Brown strongly believes Sestak can beat Specter in the primary: “The only caveat is that he needs to continue raising substantial sums of money, so that he can buy the advertising time.”

That cash also will allow him to do other marketing, such as mail pieces and maybe billboards, to help him become better-known outside of Philly and her suburbs.

Sestak has significant structural advantages that likely were part of his decision-making.

First, Pennsylvania has a closed primary. This is incredibly important, because liberal Republicans (and Republican-leaning independents registered with the GOP) may have been inclined to stick with Specter but cannot vote for him against Sestak – unless they change their party registration.

While some may do so, it is doubtful enough will to change the outcome. Most will want to remain registered Republican, to vote in the party's gubernatorial and Senate primaries.

Unlike last year’s presidential primary, when some party-switching occurred, a few exciting races will be on the GOP side next year, Brown says. Besides, few Republicans will feel that committed to Specter, who abandoned their party and was disloyal on numerous votes before that.

Second, this is a midterm election – incredibly important because of who generally turns out. Those voters are different than ones who turn out in a presidential year; typically, it is smaller, more partisan and more politically engaged electorate.

“This helps Sestak tremendously,” Brown notes. “Essentially, the primary electorate will be made up of loyal Democrats who have most likely voted five times against Specter in general-election contests since 1980. Why in the world would they want to vote for Specter now?”

Specter has a tougher case to make to these folks: It boils down to, "Forget all of our electoral history and vote for me because Rendell and Obama like me."

Sestak's argument is more straightforward and more appealing: "I'm the best Democrat in this primary, so vote for me."

He also is a good fit for the state. He’s a moderate Democrat with a military background. He has a large family that can act as surrogates around the state and help create "personal" connections. And he has a national profile – having served as a national security adviser in Clinton's administration – which will help him raise money in places such as New York and California.

As for his “netroots,” Markos Moulitsas, publisher and editor of the Daily Kos, assures that plenty of money will flow to Sestak once he files.

Should Sestak win both the primary and the general election, he will not owe his seat to the party leadership, allowing him to buck that leadership (if he wants to) on Senate votes.

“That would put him in a great position to be able to craft a legacy that is independent of his party,” notes Brown.

That’s an advantage for Pennsylvanians, enabling him to better represent the state's interests than most senators who make it to Congress.