White House aides were reportedly caught off guard by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE's informal phone call with Canadian Prime Minister Justin Trudeau, learning about the call only after Canada's foreign ministry published a readout.

The Washington Post reports that Trump began handing out his personal cellphone number to a few world leaders shortly after his inauguration, including to the leaders of Mexico and Canada, and that Trudeau took advantage of the opportunity to call the president in April 2017 to speak about trade issues.

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White House aides, according to a senior U.S. official who spoke to the Post, were totally unaware that the call had even occurred.

“We had no idea what happened,” the official said.

The White House would later put out a short readout of the call based on Trump's memory between the two leaders, according to the Post.

"The two leaders discussed the dairy trade in Wisconsin, New York State, and various other places. They also discussed lumber coming into the United States," the full White House release said. "It was a very amicable call."

A much lengthier Canadian readout from the call stated that the pair discussed dairy trade between the two nations, which Canada said “heavily favors the U.S.”

The Associated Press reported last year that Trump had also given his cellphone number to French President Emmanuel Macron, but noted that Macron's office would not comment on whether the French leader planned to actually use the line.

White House aides urged Trump to route future calls with world leaders through the White House Situation Room, as required by federal records law, according to the Post, and there are no other confirmed calls between Trump and world leaders on his personal cellphone.

A group of Senate Democrats asked the president's counterintelligence chief in June for a threat assessment on Trump's cellphone usage, which they called "reckless" and a danger to national security in a letter.

"We are especially concerned about recent reporting that President Trump has eschewed the advice of counterintelligence experts and opted to use unsecured commercial devices for telephone calls and internet use. We believe this conduct is reckless and could endanger sensitive U.S. national security interests," the Democratic senators wrote.