President Donald Trump’s confirmation Sunday that the United States may accept a presidential aircraft gifted from Qatar marked the latest escalation in his clash with Boeing, which is years behind on its government contract to build the new Air Force One.

"They're giving us a gift," Trump told reporters at the White House on Monday, adding that he would be "a stupid person" if he did not accept it.

Critics have since pointed to a clause in the U.S. Constitution prohibiting officials from accepting gifts from “any King, Prince, or foreign State” without congressional approval.