Possibly true IF Specter ever runs for re-election.
Right now, Specter will probably be retired in 6 years and could care less what Bush or the GOP thinks of him.
Arlen is working on his own legacy now.
Yes and no. The GOP can still change the senate rules and Arlen could lose his chairmanship of the judiciary. There are an awful lot of conservatives to whom Arlen is deeply indebted for his reelection. Santorum, whose seat is in jeopardy anyway, can just write this election off if Bush nominates a "moderate", or if Arlen protests a conservative. Arlen is too much a part of the old boy network to turn his back on his friends now.