Because of Senate procedures that require at least one minority party member to agree to move a nominee out of committee, Arlen Specter's defection to the Democrats may hinder Obama's ability to nominate an extreme leftist to the Supreme Court.
When Obama nominates a replacement for retiring pro-abortion Supreme Court Justice David Souter, that nomination will head to the Senate Judiciary Committee for hearings and a vote.
The committee requires the consent of at least one Republican to end debate and move a nominee to the full Senate for a vote.
Specter, the former ranking minority member of the Republican Party on the committee, would have been the most likely GOP lawmaker to sign off on Obama's nomination.
Without his presence and vote, the rest of the members of the GOP on the panel could band together to oppose a pro-abortion nominee and prevent the confirmation process from moving ahead. In such a case, Democrats would likely have to present a motion to change the Senate's rules to block the option of the minority to exercise its opposition -- a move that could result in significant political fallout.
As the majority party the Democrats can change the procedural rules of the Senate, but they may not be eager to open that can of worms.