A knowledgeable D.C. source says:

Shannen’s right about the floor scheduling piece. Specter has told people privately (that he will determine whether or not to have hearings on re-nominated Appellate nominees “on a case by case basis.” He says he will have a hearing in those cases where he thinks it will be helpful to secure confirmation and not hold another hearing where it would be unproductive. Pryor falls in the latter category. When the Committee reports out the nominees, it’s the Senate Leader’s job to schedule.
Senate sources also think that once the Senate completes action on the Budget (mid-April) and the Democrats have continued to filibuster, Frist will pull the trigger on the constitutional (51 vote) test and let the chips fall where they may. Specter trying to avoid that showdown, but it’s out of his hands.