On paper, Sestak might seem like a long-shot, but yet he's clearly convinced that a primary against Specter could succeed...so what does Joe know that we don't? Last week I speculated about the existence of internal polling that shows Specter vulnerable to negative messaging.

Over at TPMDC, Beutler posts an interview that redoubles my suspicion:

[Sestak] 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."

Bet money that Sestak's already poll-tested those attacks against Specter, and that they proved effective. If there's enough money behind this primary to get that message out, Arlen's happy numbers from last week might nosedive fairly quick.