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Olympic swim trials commence in Omaha, Neb.

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Michael Phelps competes in preliminary heat 10 of the Men's 400 m Individual Medley during the 2012 U.S. Olympic Swimming Team Trials at CenturyLink Center in Omaha, Neb. on June 25, 2012.

David Phillip / AP

Peter Vanderkaay swims in the men's 400-meter freestyle preliminaries.

Mark Humphrey / AP

William Nicely, from left, David Ingraham, Nolan Tesone and Stephen Schmuhl swim in the men's 400-meter individual medley preliminaries.

Although Michael Phelps dominated in Beijing, Ryan Lochte is proving to be a formidable challenger. The 27-year-old, who has trained nonstop for the past four years, is focused on London. He's beaten Phelps, but never at the Olympics. NBC's Kevin Tibbles reports.

Read about the trials here

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