The U.S. Olympic swim team has a history of improving its times from the trials to the games.
The Americans are counting on it happening again next month in Rio after not setting a single world record during the eight-day selection meet.
Led by Michael Phelps and Katie Ledecky, the U.S. still boasts the most powerful swim team in the world.
But other countries have improved since four years ago in London and Phelps knows he's got to be much better by the time the Rio Games begin.
Clearly, there's cause for concern.
Many of the times swum in Omaha were slower than the 2012 trials, where no world records were set. Ryan Lochte and Missy Franklin struggled...