U.S. Olympic swim champions conquer challenges to win at Winter Nationals

Michael Phelps, Missy Franklin, Allison Schmitt and Dana Vollmer all won individual Olympic gold medals in 2012 and then dealt with unique challenges to their dominance in this Olympic cycle.

On Friday, all four captured U.S. Winter National titles in events where they reigned in London.

Start with Phelps, the 22-time Olympic medalist who last year came out of a 20-month competitive retirement and then was suspended following a September 2014 DUI arrest.

On Friday, Phelps clocked 51.38 seconds to win the 100m butterfly at the U.S. Winter Nationals in Federal Way, Wash. That’s his fourth-fastest time ever outside of summer meets in the event, which he’s won at the last three Olympics, according…