The problem is, that the longer they wait to run a filibuster, the worse their political problem the next time, on the next nominee.
Suppose, for example, Ginsberg or Stevens were to leave the Court, and The President were to replace that person with someone even as "moderate" as Kennedy --- that would really cook the liberal goose - yet could they filibuster such a candidate? (Suppose for purposes of this discussion, judicial philosophy of Gonzales...)
Their problem is right now... with this nomination ... the next one may be too late because even a moderate justice may well hose them.
I don't think he'll do that, though. His short list was Miers, Alito, and Luttig. Miers blew her chances by failing to wow the senators in personal visits, and Bush doesn't give second chances. He never has.
I'd have to say that unless something new comes up with Luttig, he's the choice to replace Ginsburg or Stevens if neither is able to outlast the Bush Presidency.
A lot depends one whether another vacancy occurs before or after the 2006 elections and whether that changes the senatorial lineup.