Supreme Court Justice Sandra Day O'Connor announced her resignation today, surprising most of the media that had been maintaining its vigil over the ailing, octagenarian Chief Justice.
While President Bush in his statement this morning said he would not nominate a successor today, his choice will come soon, likely after his upcoming European trip. But the President already fired a shot across the bow of Senate Democrats, signaling his willingness to test the filibuster compromise:

The nation deserves, and I will select, a Supreme Court Justice that Americans can be proud of. The nation also deserves a dignified process of confirmation in the United States Senate, characterized by fair treatment, a fair hearing and a fair vote.

The war over the direction of the Supreme Court actually consists of three distinct battles:

• The Nominees and the Judicial Filibuster. While much has been made over the Democrats' use of the judicial filibuster for lower court appointments, it is unlikely to come to that for SCOTUS. Unless President Bush chooses a blatantly partisan hack like former Solicitor General, Federalist Society cheerleader and Bush v. Gore legal eagle Ted Olsen, it will be politically difficult for Democrats to seek to block most on the Bush short list. (For a good run down of the likely nominees, see Jeffrey Rosen in The New Republic or the SCOTUS blog.)
• The Choice Issue. Virtually all eyes in the progressive camp have been on Roe v. Wade and the issue of reproductive rights. Again, Democrats have very little leverage here; it is virtually certain that any nominee sent to the Senate will be pro-life. As many (again, see the Rosen piece) are formidable legal minds, blocking them will not be an option. (Whether a new pro-life Court would actually undo Roe v. Wade is a separate discussion altogether.)
• States' Rights and the "Constitution in Exile." As I wrote in "Sharpening Their Clause", the new wave of Bush judicial picks may dramatically redefine the scope of federal power relative to the states. With their narrow reading of the Commerce Clause, these jurists may sharply curtail Washington's regulatory powers in environmental, health, workplace safety and other areas they see as having been invented without constitutional foundation since the days of FDR.

All in all, it will be a barn-burner.