(CNN) President Donald Trump paid sober tribute to victims of crashed Flight 93 in Pennsylvania on Tuesday, the anniversary of the September 11 terrorist attacks.

"This field is now a monument to American defiance," Trump said in remarks near where the aircraft went down 17 years ago. "This memorial is now a message to the world: America will never, ever submit to tyranny."

It was a message of defiance in the face of terrorism, delivered by a New Yorker president who has at times struggled to adopt the role of consoler in chief.

The President began the day on a combative streak, tweeting angrily about the Russia investigation from the White House as mourners were gathering in lower Manhattan, at the Pentagon and in the Pennsylvania field where Flight 93 crashed 17 years ago.

When he arrived in Pennsylvania with the first lady, Trump flashed a celebratory smile and pumped his fists as he greeted supporters on the tarmac in Johnstown, Pennsylvania.

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