Carolyn Lochhead of the San Francisco Chronicle reports:

Gerald Pomper, a Rutgers University political scientist, expects Obama to make his choice first, probably before the Summer Olympics begin Aug. 8 in Beijing. If he waits until after the Olympics, he will run into his convention, which starts Aug. 25, and he may want to allow time for any furor that could result if he fails to nominate Clinton to die down.

McCain has the advantage because the Republican convention comes second, the first week in September, and he will be able to choose his running mate in response to Obama's.