We cannot lose the Senate whatsoever. The reason that we haven't seen any Supreme Court retirements in Bush's term is because of the firestorm that would erupt in the Judiciary Committee and the filibustering that would occur on the Senate floor. The Justices have been patiently waiting for the Republican margin in the Senate to increase. A Democrat-controlled Senate would make all of that futile. A Specter-led Judiciary Committee would not be as bad as that, but still not ideal.
One can only hope that a Bush-Santorum endorsement came with some serious strings attached, and that if Specter steps out of line in his new term that he will be severely and publicly rebuked by the White House and banished from all future insider meetings (politically castrated).
-PJ
We do a lot of "hoping" or waiting for supermajorities or compromising or whatevering. I hope (or wish) the Pubs could have the discipline our opponents have. Just like war or business, it's about will.