Swimmers compete in the men's 50-meter freestyle preliminaries at the U.S. Olympic swimming trials, Saturday, June 30, 2012, in Omaha, Neb. (AP Photo/Nati Harnik)

Anthony Diers dives at the start of a heat in the men's 50-meter freestyle preliminaries at the U.S. Olympic swimming trials on Saturday, June 30, 2012, in Omaha, Neb. (AP Photo/Mark Humphrey)

Jimmy Feigen, top, and Josh Schneider swim in the men's 50-meter freestyle preliminaries the U.S. Olympic swimming trials, Saturday, June 30, 2012, in Omaha, Neb. (AP Photo/Nati Harnik)

Anthony Ervin reacts after swimming in the men's 50-meter freestyle preliminaries at the U.S. Olympic swimming trials, Saturday, June 30, 2012, in Omaha, Neb. (AP Photo/Mark J. Terrill)

Cullen Jones reacts after swimming in the men's 50-meter freestyle preliminaries at the U.S. Olympic swimming trials, Saturday, June 30, 2012, in Omaha, Neb. (AP Photo/Mark J. Terrill)