What comes next: Filling a Supreme Court vacancy

Now that Justice David Souter has helped solve the mystery of whether anyone would retire from the Supreme Court this year, what's next? How will the executive and legislative branches of government set about filling a vacancy on the nation's highest court?

- President Barack Obama will have to nominate a successor after Souter makes his retirement announcement official. Souter is likely to stay on the court through the end of the term in June, and maybe longer if a replacement is not quickly confirmed. Obama will have chosen his successor long before June - if the president hasn't already made up his mind - but an announcement from the White House is unlikely before the Supreme Court finishes this year's session.

- The Constitution requires the president to submit his nomination to the Senate for its advice and consent; the House plays no role. The Senate's majority Democrats and minority Republicans will investigate the nominee's background thoroughly before hearings begin in the Senate Judiciary Committee. It normally takes between four and six weeks to begin hearings after the Senate receives a Supreme Court nomination.

- The Senate will try to hold hearings and a confirmation vote before the Supreme Court begins its new term in October.

- Hearings will be supervised by Judiciary Committee Chairman Patrick Leahy, D-Vt. Following Pennsylvania Sen. Arlen Specter's defection to the Democratic Party earlier this week, GOP committee members will have to elect a new top committee Republican. Sen. Orrin Hatch, R-Utah, has served as chairman before, and would need a waiver from members to serve again. Next in line would be Sen. Charles Grassley, R-Iowa. Senate hearings on the nominations of John Roberts as chief justice and Samuel Alito as justice, the high court's two newest justices, lasted about a week.

- At the end of hearings, the committee will vote on the nominee and send a recommendation to the full Senate. Whether the committee decision is positive or negative, the full Senate is likely to vote on the nomination.

- It takes 60 votes to block a filibuster of a Supreme Court nominee. Democrats now hold 59 votes in the Senate with Specter's defection and two Democratic-voting independents. There is one open seat in the Senate with Norm Coleman and Al Franken fighting in court over the right to be the Minnesota senator.