For all you political junkies smacking your lips at the prospect of a good fight, the impending Pennsylvania clash between Arlen Specter and Joe Sestak figures to be a hot fudge sundae with cherry on top.

This contest for the 2010 Pennsylvania Democratic senatorial nomination may prove to be unhealthy for the Democratic party, but, that aside, the nine-month bumper-car collision that officially began this morning is bound to be highly entertaining:

Snarlin' Arlen versus the Three-Star Admiral.
The Insider versus the Outsider.
The Party Establishment's Choice versus The Upstart Who Won't Go Away.
The Guy Who Joined the Democrats in '09 versus The Guy Who Joined the Democrats in '06.

Sestak made his challenge official this morning. Finally. For months he had teased and flirted, claiming that he first had to consult with his wife, his father, his daughter, his pet hamster, the neighbor's dog...but now he has honed his pitch. He said that in 2008, "this nation voted for change and accountability," and that he expects Pennsylvania's Democratic voters to do the same in the Senate primary next spring. Translation: Even though Barack Obama has already endorsed Specter the turncoat, Sestak considers himself to be the more authentic Democrat and hence the true heir to the Obama message of change. In short, he will try to frame the primary as a party loyalty test.

Well in advance of the spring contest, incumbent Specter is trouncing Sestak in the polls, but that's no surprise, given their name ID disparity. Specter has been a statewide fixture for nearly 30 years, while Sestak (a career Navy man until 2006) has only been a suburban Philadelphia congressman for two and a half years. My assumption is that Sestak will narrow that 30-point polling gap considerably as the months pass; he certainly has the money to do so. At the end of June, Sestak had $4.3 million in the kitty - in contrast to Specter's $7.6 million - with the prospect of raising much more from grassroots Democrats who view Specter as little more than an opportunist who quit the GOP only because he would've been road kill had he stayed. (Assuming Sestak can raise money, he can use it to upgrade his website. His announcement today was streamed live, but he sounded as if he was gargling nails at the bottom of a well. The partial quote in the previous paragraph was all that I could make out.) 

Most importantly, Sestak at minimum will be a major irritant for Specter during the next nine months. Specter is already viewed by many Pennsylvanians as essentially conviction-free, a weathervane who blows with the prevailing winds, and Sestak's challenge will worsen Specter's image woes.

Since only registered Democrats can vote in the 2010 primary, Specter will be forced to move to the left in order to mollify the liberal base and trump Sestak's charge that the incumbent is a faux Democrat. For instance, watch how Specter tries to present himself as an ally of the proposed law that would make it easier for labor unions to organize. He'll need to do that, in order to ensure that the labor unions won't endorse Sestak.

What's noteworthy, of course, is that, as recently as a few months ago, when Specter was still a Republican, he indicated publicly that he favored blocking Senate consideration of the proposed law making it easier for labor unions to organize. At the time, he was facing a conservative Republican primary challenge from Pat Toomey...which meant that he was being forced to move to the right in order to mollify the conservative base.

Back when Specter had to worry about his right flank in the GOP, he voted for the Bush tax cuts and other conservative favorites. As recently as March, when he was still a Republican and worried about Toomey's challenge, he sided with the Democrats on contentious Senate votes only 16 percent of the time (according to Nate Silver, the respected numbers-cruncher). But once he became a Democrat this spring, and started worrying about a Sestak challenge, he has sided with the Democrats on contentious Senate votes a whopping 97 percent of the time.

Perhaps Specter's constant re-calibrations can be spun (by Specter allies) as evidence of his responsiveness to the voters. Or his behavior can be spun as Sestak no doubt intends - as evidence that Specter is a congenital flip-flopper with no fixed convictions. That's why Specter surely views Sestak as a pain in the butt. Even if Specter ultimately wins the Democratic primary, his leftward tilts in 2009 will be cited by Pat Toomey during the general election as fresh evidence that the formerly rightward-tilting Specter cannot be trusted.

So in the short run, we can expect Specter to get personal and seek to paint Sestak as a fraud; at all costs, Specter has to ensure that the liberal Democratic base doesn't flock to his foe. And Specter has already signaled this tactic. Last month he assailed Sestak as "a flagrant hypocrite" who didn't even register as a Democrat until 2006, "just in time to run for Congress." Sestak said in response that, as a career military man, he had opted to remain nonpartisan; however, "I voted for Bill Clinton, Al Gore, John Kerry and Barack Obama while Arlen Specter was voting for George Bush and Bob Dole and John McCain." (Nobody can predict what the spring '10 political mood will be, however. Specter boasts that he has Obama's endorsement, while Sestak boasts that he voted for Obama. Will the Obama imprimatur be an asset in Pennsylvania next spring?)

Specter is one tough hombre, and at minimum Sestak will need to demonstrate that he can take a punch. But I doubt that a guy who led a Navy aircraft carrier battle group in the Afghanistan war will have trouble handling even the nastiest rhetorical weaponry. Let the games begin.

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"You know, honey, I'm sick to death of this socialist Obama and those socialist Democrats using government to meddle with our lives."

"Me too, dear. Would you like me to put on Fox News? Or maybe we can go to that town hall meeting today and shout down our Democrat congressman. I can go online and get planning tips from those pro-American national groups on how we can act spontaneous."

"Maybe later, honey. First I've gotta take our old gas guzzler over to the showroom so that I can take advantage of that sweet cash-for-clunkers deal."

"But dear, I hear the money is running out."

"So help me, if that Democrat congressman doesn't put more government bucks into that clunkers program, I'm gonna chase him down the street!"

"Yes, we could make a placard. 'Keep your hands out of my clunkers program!'"

"No, honey, it's the opposite, we want them to...oh never mind, let's just go shout at the socialists."