Justice John Paul Stevens said to be retiring

The Supreme Court is about to undergo another generational transition, as the senior leader of its liberal wing, John Paul Stevens, is expected to retire this summer and be replaced by a junior justice appointed by President Obama.

For the moment, the front-runners for the nomination, assuming Stevens does announce his retirement after he turns 90 next month, are said by legal insiders to be U.S. Solicitor Gen. Elena Kagan, 49; Judge Diane Wood, 59, of the U.S. 7th Circuit Court of Appeals in Chicago; and Judge Merrick Garland, 57, of the U.S. Court of Appeals for the District of Columbia Circuit.