This will obviously give Barack Obama his first court pick.
Clearly, Souter's legacy was in being yet another missed opportunity for a Republican president to move the court to the right.
In 1992, for example, Souter provided the pivotal fifth vote for abortion in the famous Planned Parenthood v. Casey decision.
The fact that Souter -- who, at 69, is far from the oldest member on the court -- has chosen to depart so early in Obama's term (as opposed to late in Bush's term) -- underscores the mistake George H.W. Bush made in appointing him to the bench.
Bush Chief of Staff John Sununu vouched for Souter's conservatism and persuaded Bush to appoint him.
The good news for conservatives is that, because Souter was so liberal, his departure is unlikely to change the makeup of the court. It does, however, give Obama the opportunity to pick an even younger Justice who might be around for many years to come.
There is speculation that Obama will appoint a woman to replace Souter.