The US President was taking questions from reporters at his golf club in New Jersey on Saturday about four executive orders signed for coronavirus relief when a reporter questioned his claim.
Mr Trump said: "We passed Veteran's Choice and Veteran's Accountability. They've been trying to get that passed for decades and decades and decades and no president's ever been able to do it, and we got it done."
But Paula Reid of CBS News asked him: "Why do you keep saying that you passed Veterans Choice?"
Mr Trump tried to move onto questions from another reporter, but Ms Reid pressed him, asking: "You said that you passed Veterans Choice. It was passed in 2014... it was a false statement, sir."
The Veteran's Choice law allows eligible veterans to be covered by the government for care provided by doctors outside the main veterans healthcare system.
The bipartisan act was signed into law by President Barack Obama in 2014 and spearheaded by Democratic Senator Bernie Sanders and the late Republican Senator John McCain.
Mr Trump signed a different law in 2018 that expanded the Veterans Choice programme. He has reportedly made the false claim about Veterans Choice more than 150 times.
He replied to Ms Reid: "OK. Thank you very much, everybody," before storming out as the pop song "YMCA" played.