Golden Tempo won the Kentucky Derby on Saturday, making Cherie DeVaux the first woman to train the winner of the opening leg of the Triple Crown.
"Only in these days of political correctness could such an overturn occur," Trump tweeted.
Country House, a 65-1 long shot, was declared the Kentucky Derby winner after first finisher Maximum Security was disqualified.
In 1968, a drug test led officials to controversially disqualify Kentucky Derby winner Dancer's Image.
The business community near Santa Anita Park is expected to take a financial hit after racing was suspended indefinitely.
Triple Crown champion Justify paid a visit to Santa Anita Park on Saturday, sauntering around the track between races before taking photos in the winners' circle.