When Rep. Joe Sestak (D-PA) makes his primary challenge to Sen. Arlen Specter (D-PA) official, he won't have the Washington establishment on his side and he'll probably find himself significantly outspent by his famous opponent. But he has some tricks of his own up his sleeve.

"If you have the right message, and you're consistent in putting it out there," Sestak told me, then you still have a shot. "Sen. Clinton, running against Sen. Obama, was outspent four-to-one in Pennsylvania and yet somehow her message seemed to resonate." *

He describes "the message" as a key issue. But what will his message be? In an interview with TPMDC, Sestak provided some clues.

"Arlen has spent the last three decades in Washington as a senator and has a lot of experience in the Washington senatorial establishment," Sestak said. "The same one that made a deal with him."

By contrast, "I come from 31 years in the military."

Furthermore, Sestak says Specter's record will haunt him. "I went to Washington to oppose the policies of President Bush," he says by way of contrast to Specter who "supported them."

A few weeks ago, Sestak told me that Specter would need to prove himself a reliable Democrat on key issues if he wanted to avoid a challenge, but ultimately he decided that Specter just can't be trusted.

"[W]hen you see someone who has voted so consistently with President Bush--I think it's four out of five times--that voted on issues that have been very instrumental in terms of harming our national security...or for the economic policies of the Bush administration.... That raised even graver doubts about how is he going to now forsake those kinds of beliefs in any consistent way."

Sestak went on. "I think the fact that the change was now, rather than several years ago when our nation could have used more Democratic votes to help forestall some of the policies of President Bush. That would have been a more telling party switch."

As I noted last week, Sestak already has a key supporter in Pennsylvania--former Rep. Joe Hoeffer, who challenged Specter in 2004. I asked Sestak how he felt about the endorsement and he lit up. "I feel very honored," he said.

*Due to a transcription error, this quote initially misstated Sestak's comments on the 2008 Pennsylvania primary. As Rep. Sestak suggested, Hillary Clinton--and not Barack Obama--won that race.