Trump was pictured grimacing as he made the triumphant gesture shortly after touching down in Shankville, Pennsylvania, near where United Flight 93 crashed after it was hijacked by four Al_Qaeda terrorists on board, as part of the tragic September 11 attacks.
Stephanie Tittle blasted Trump for the signal, tweeting: This is not an exclamation point day. This is not a fist pump day. You sully the solemnity of this day. History will not be kind to you.
"But we will #NeverForget those who lost their lives and those who gave so much to help so many on that day, and the days that came after."
ML Cliff wrote: "Trump does fist pump en-route to #Shanksville Memorial Ceremony – This shines a spotlight on @realDonaldTrump INABILITY to feel #empathy for another person’s loss; and his avoidance of #NYC #September11th memorial reflects his inability to admit any weakness #Trump."
Jim Harris also reacted, writing: "So the clueless, soulless phony-in-chief arrives on hallowed ground, attempting to portray a decent human being, and fails again. He defiles every space he inhabits. To those who lost loved ones on 9/11, we wish you peace and love."
Earlier on Tuesday, Trump also raised eyebrows with a tweet commemorating the anniversary.
He wrote: "17 years since September 11th!"
But people felt the tweet was too insensitive and could have been better worded, especially coming from a President.