It is pretty obvious that before 2009 the President will have to fill several vacancies on the Supreme Court. It was one reason the last Presidential election was fought so hard. The current cohort of nine has served together longer than any other. At least three are unlikely to remain in office until President Bush's successor takes over. Since the three are Rehnquist (one of the most reliable conservatives), Stevens (one of the most reliable liberals) and O'Connor (often the swing vote) it is not only the case that the President can potentially swing the court is his chosen direction, but that a President Kerry could have taken the opportunity to swing it in an opposite direction.
So what is the President's chosen direction? The lazy division of justices into 'liberal' and 'conservative' - a trap I fell into above - obscures the real differences within both camps. Fortunately, a recent case on medicinal marijuana (Gonzales v Raich) exposed some of these divisions and may inform the debate.
Rehnquist and O'Connor both found themselves opposing the majority decision. Typically, in both cases, they took a states' rights position, opposing the effort by the Federal government to infringe the right of the states to allow the use of marijuana. Though O'Connor has been heavily criticised by conservatives for her views on affirmative action (among other things) her support of states' rights has been consistent. Indeed, partly because of O'Connor's usual role as the swing vote, support for division of power outlined in the 10th amendment has perhaps been the most consistent theme of the Rehnquist court.
If both O'Connor and Rehnquist are replaced by justices less committed to the 10th amendment the cause of federalism will take a serious blow. And this is possible. The victor in Gonzales v Raich was the Bush administration. Despite his background as a state governor, there is no evidence that Bush is especially committed to the 10th amendment. Antonin Scalia, who found himself lining up against his normal conservative allies (Rehnquist, O'Connor and Thomas), was siding with the President when he concurred with the majority opinion.
The President has previously said the justices he most admires are Scalia and Thomas. By siding with the administration in this case, Scalia may have increased his chances of becoming Chief Justice at the expense of Thomas. Some commentators have suggested that this was his purpose, though that is partly to ignore the real philosophical differences between Scalia and Thomas.
Broadly, Thomas is a textualist (not, as is often stated, a strict constructionist). The text of the constitution is his ultimate legal compass, though he looks for a reasonable interpretation of the text and not for the strictest possible interpretation. Scalia looks principally to Supreme Court precedent as his guide, unfortunately this means that when the Supreme Court makes a flawed ruling it will become locked in stone. One example would be the 1896 ruling in favour of segregation, Plessey v Ferguson, which took over 50 years to overturn.
In passing, it is worth noting that the majority in Gonzales v Raich were not merely reasserting previous federal transgressions against the states, but greatly extending the basis for future transgressions, and even from a point of view of precedent, the majority and concurring judgements can be criticised on these grounds.
Bad news for the 10th amendment might involve appointing Ted Olsen, author of the Patriot Act, to the Supreme Court. This might also, by the way, be bad news for Antonin Scalia, as Olsen is a jurist of sufficient weight and prominence to appoint directly as Chief Justice, something that would save the President a separate confirmation in the Senate. Good news for the 10th amendment might be the appointment of Janice Rogers Brown and the promotion of Clarence Thomas to Chief Justice. Among other things, this would seem to show that the states' rights position, often associated with segregation in the past, is a wholly integrationist one today.