U.S. President Donald Trump talks with Canada's Prime Minister Justin Trudeau during a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, Britain, December 4, 2019. The NATO summit came to an end with U.S. President Donald Trump leaving earlier than scheduled and canceling a final news conference on Wednesday, saying he had briefed the media many times during his two-day trip. REUTERS/Kevin Lamarque

U.S. President Donald Trump and Canada's Prime Minister Justin Trudeau shake hands during a meeting ahead of the NATO summit in Watford, in London, Britain, December 3, 2019. Earlier in the day Trump called Canadian Prime Minister Justin Trudeau "two-faced" after a video surfaced of Trudeau talking with the leaders of Britain, France and the Netherlands about Trump's team's jaws dropping "to the floor" during an impromptu news conference with the two leaders. REUTERS/Kevin Lamarque

U.S. President Donald Trump and Canada's Prime Minister Justin Trudeau hold a meeting ahead of the NATO summit in Watford, in London, Britain, December 3, 2019. At a final news conference, Trudeau played down the incident, saying he and Trump had enjoyed a great meeting and that the jaw-dropping comment was a reference to the announcement of the location of the next meeting of G7 leaders at the U.S. presidential retreat, Camp David. REUTERS/Kevin Lamarque

U.S. President Donald Trump and Canada's Prime Minister Justin Trudeau hold a meeting ahead of the NATO summit in Watford, in London, Britain, December 3, 2019. By the time the summit wound up on Wednesday, Trump had decided not to hold a final press conference, saying he had already said enough. REUTERS/Kevin Lamarque

U.S. President Donald Trump talks with Canada's Prime Minister Justin Trudeau during a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, Britain, December 4, 2019. The half-day summit at a golf resort on the outskirts of London was always going to be tricky, with officials hoping to avoid bust-ups that burst forth at their meeting last year when Trump complained about allies failing to bear the financial burden of collective security. REUTERS/Kevin Lamarque

U.S. President Donald Trump talks with Canada's Prime Minister Justin Trudeau during a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, near London, Britain, December 4, 2019. Earlier in the day Trump called Canadian Prime Minister Justin Trudeau "two-faced" after a video surfaced of Trudeau talking with the leaders of Britain, France and the Netherlands about Trump's team's jaws dropping "to the floor" during an impromptu news conference with the two leaders. REUTERS/Kevin Lamarque