While it is likely that President Obama will have to fill a Supreme Court seat during his term, it will almost certainly be to replace one of the more liberal members of the court. If moving the court to the left is a priority at all for the Obama administration, then he should appoint someone is more liberal than the person that judge replaces. However I find it highly unlikely that such a thing would happen. The freak-out from the right over the appointment of someone more liberal than, say, John Paul Stevens would likely be more than a post-partisan administration could handle. The press assaults would be deafening and concrete assertions about how a justice would rule on issues would be pressed for in a way unseen with Alito or Roberts, to say the least. I’d love to be proven wrong, but in the early going of the Obama administration getting things done seems to be a higher priority than getting things done along a particular ideological line.