As has been widely reported, one of Arlen Specter’s potential Democratic challengers, Rep. Joe Sestak, doesn’t sound intimidated by his party’s embrace of the former Republican. Sestak is a retired Navy admiral who was first elected to the House in the 2006 Democratic sweep. But though he was a determined foe of the Iraq War — the key Democratic issue that fall — his victory had a lot more to do with the ethical scandals plaguing Rep. Curt Weldon, the man he defeated.

Though something of a political novice, Sestak is articulate and a hard worker. And he is popular on the Left because of his anti-war positions. That will stand him in good stead if he decides to risk a relatively safe House seat in the hopes of defeating Specter in a Democratic primary.

But though such a primary is almost a year away, you can bet that the wily Specter will unearth one particularly unpleasant skeleton in Sestak’s political closet if the two clash.

Back in the spring of 2007, Sestak spoke at a fundraiser for the Philadelphia branch of the Council on American Islamic Relations (CAIR). The decision (which Sestak subsequently blamed on the inexperience and incompetence of a staffer who, it turns out, was herself a former CAIR activist) caused Sestak no end of trouble with his Jewish constituents. They, not surprisingly, took a dim view of their congressman helping to raise money for a group that was founded as a Hamas front organization. Though he knew it was a political mistake, Sestak chose to disregard the evidence of CAIR’s criminal involvements. CAIR’s involvement with the Holy Land Foundation, a group that raised money for Hamas, was brought up in court during the successful federal prosecution of the the latter group.

Despite pressure to cancel, Sestak went ahead and spoke at the fundraiser. Since then he has gone out of his way to express support for Israel and the local Jewish community at every possible occasion. And since the GOP was unable to raise enough money to give his Republican opponent a fighting chance in 2008, local pro-Israel activists either sat out the race or supported Sestak.

This incident may not deter Sestak’s fans on the left, including the MoveOn.org types who likely can’t stomach Specter and are hardly pro-Israel stalwarts. But you can bet that if Sestak decides to challenge Specter, the former admiral’s evening with CAIR will be featured in the senator’s efforts to discredit his opponent.