Supreme Court Vacancy?

In the last year, much of the general talk about U.S. Supreme Court vacancies has centered around Justice Ginsberg (due to poor health) or Justice Stephens (due to his age). However, there is now speculation that Justice Souter is planning to retire.

If so, does that increase the likelihood we will see two vacancies?

If any of these three retire, the ideological composition of the court will remain unchanged, as President Barack Obama will replace one liberal activist with another. However, the retirement of Justice Souter would almost certainly raise the intellectual heft of the court, as he is the court's weakest link.