The Pennsylvania Senate race has had its share of accusations of political shenanigans, if not illegal behavior. First, there was the suggestion that the White House was offering Rep. Joe Sestak a job to get out of the race. Now this:

Rep. Joe Sestak’s Senate campaign seized on a statement by former GOP Sen. Rick Santorum Saturday that he traded his 2004 endorsement of Sen. Arlen Specter for a promise that the senior senator would support President Bush’s judicial nominees.

“The reason I endorsed Arlen Specter is because we were going to have two Supreme Court nominees coming up,” said Santorum, responding to a question at the Southern Republican Leadership Conference in New Orleans. “I got a commitment from Arlen Specter that no matter who George W. Bush would nominate, he would support that nominee,” he added.

Sestak’s campaign called it “one of the most glaring red flags” that has come to light about Specter to date.

Is Santorum describing a quid pro quo — a deal in which Specter was to ignore his obligation to examine Supreme Court justices? (Recall that this would have applied to Harriet Miers had she not withdrawn.) Specter denies there was any deal, and there is no way in the he-said-he-said tussle to discern whether it is Santorum or Specter who is telling the truth. Santorum has every reason to try to sink Specter; Specter has every reason to deny the allegation.

It does, however, point to the greatest problem Specter may face — the obvious lack of principle and loyalty, the infinite flexibility. The only fixed principle is, apparently, “do whatever benefits Arlen Specter.” This time around, his opportunism may backfire. It may turn out that he picked the wrong time to run as a Democrat. It would be a fitting lesson in the limits of political expediency.