As the nation remembered the thousands who died 17 years ago Tuesday, President Donald Trump started out his day tweeting about the Russia investigation and pumping his fists before a solemn memorial service.

The president's first Twitter post of the day appeared to quote Fox News and took on the Russia investigation.

"We have found nothing to show collusion between President Trump & Russia, absolutely zero, but every day we get more documentation showing collusion between the FBI & DOJ, the Hillary campaign, foreign spies & Russians, incredible," the president wrote, citing Lou Dobbs, a Fox Business anchor, and Sara Carter, a contributor.

He posted two other tweets attacking the FBI and Justice Department in between marking the somber anniversary on Twitter then giving an emotional speech in Pennsylvania honoring passengers who charged the cockpit of their plane to stop hijackers from attacking Washington, D.C.

"17 years since September 11th!" the president said in one post. He also hailed his attorney Rudy Giuliani as a "hero" for his leadership as mayor of New York when the coordinated terror attacks took down the World Trade Center.

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When disembarking from Air Force One to attend a memorial service in Pennsylvania, the president pumped his fists up in the air and greeted those gathered at John Murtha Johnstown-Cambria County Airport.

Critics were quick to take issue with the president's actions, decrying them as undignified, unempathetic and unpresidential.

"This is not a day for the usual unhinged Trump politics," former attorney general Eric Holder wrote after the president mentioned him in a tweet Tuesday. "This is a day to remember the innocent Americans we lost and the brave first responders who gave their lives. They’re the best of America and we should honor their sacrifice."

Other critics also voiced their frustration and disgust on social media.

"I give up.. why did he pump his fists on his way to the 911 event," one person posted on Twitter.

Another wrote: "I want to vomit when I see that image of moron trump pumping his fists upon arrival at the hallowed ground of the flight 93 crash. DISGUSTING. #UnfitForOffice #TrumpIsUnfit #NotMyPresident"

Some, though, pointed out the president may have thrown his fists in the air to signify resilience after the attack, which was a centerpiece to the president's remarks at the event.

"Is it possible Trump is pumping fists to celebrate America’s resilience in the face of/after the 9/11 attacks? Is it possible he’s cheering for the people coming out? The attacks were horrific, and those who were killed should be remembered and celebrated," one person posted on Twitter.

Trump, standing on the Pennsylvania field where United Flight 93 crashed on Sept. 11, 2001, said the flight and its passengers who fought back to prevent another attack symbolized "the moment when America fought back."

"This field is now a monument to American defiance," Trump said. "This memorial is now a message to the world: America will never, ever submit to tyranny."