When you think about it, Bush can nominate ANY of the judges that have been passed so far, to the Supreme Court. Democrats can't say they are "extrodinary" cirumstances because they were already passed.
When I think about it, I see a JRB filibuster being played by the donks if she is nominated to SCOTUS. Why? Well, SCOTUS makes different rulings as to what the law means, than does appeals. Because an originalist is not going to make law from the bench, and JRB is an originalist, the donks will say that putting her in the position to sit on the SCOTUS is extream, and the filibuster is justified. The RINOS, if bound by their pledge, are powerless to vote for the constitutionl option until the 106th. Nothing good will come of this. Nothing.
The bottomline is that "extreme circumstances" is not defined and gives the RINOS some wiggle room, a wiggle being inspired by plummeting numbers among conservative voters in their respective home states.