The American Constitution Society for Law and Policy was designed from the start to be a liberal counterpart to that right-wing cabal known as The Federalist Society. Just as the Federalist Society promotes an originalist view of the Constitution, the ACS promotes an anti-originalist (they prefer the term "progressive") view of the document.
ACS is consciously and enthusiastically against the qualities President Bush is looking for in a Supreme Court nominee.
All that said, it's still no surprise that supposedly-Republican senator Arlen Specter is not only hanging out with these folks, The Prowler reports that he's acting as point man for a lot of their opposition research on nominee John Roberts.
Given the fact that Specter is chairman of the judiciary committee, he's in a position to do a lot of damage to the president's nominee.
The Bush administration threw its considerable weight behind Specter's reelection campaign last time around, beating back an impressive primary challenge by someone who is much more reliably conservative.
The senator suffers no negative consequences for his misbehavior (ditto Sen. McCain), which as any parent knows virtually guarantees the behavior will continue.
At the very least, a way needs to be found to get Specter out of the chairman's seat.