"In conveying that message I used language that was inappropriate and basically lost the power of that message", he said.
He said the Canadian leader must not have realised Mr Trump had televisions on Air Force One, allowing him to monitor Mr Trudeau's news conference at the end of the G7 summit.
At a news conference in Singapore, the president said Trudeau only made his comments about not being bullied because he thought Trump was on an airplane and would not hear about them.
Trump's threat comes after Trudeau defended Canada during the G7 summit in Quebec over the weekend, saying his country "will not be pushed around" in regards to the Trump administration's tariffs on steel and aluminum.
Graham pointed to Trump's trade fight with Canadian Prime Minister Justin Trudeau as an example of what happens when a foreign leader tries to "play" Trump.
"I see the television and he's giving a news conference about how he "will not be pushed around" by the United States".
The Trump administration took umbrage at an ally publicly criticizing US policy just before a historic meeting with Kim Jong-Un.
Republican U.S. Senator Tom Cotton, however, said North Korea's leader could also face harsh words.
On Sunday morning Navarro and Trump's director of the National Economic Council, Larry Kudlow, piled on the criticisms.
"Take any husband and wife, who are trying to learn to live together and raise a family, you're going to have tensions, but usually we overcome them", Klein said. And I say, 'Push him around?
"Trump's disruptiveness is one thing, but his treatment of Canada and other US allies is unprecedented", said Roland Paris, a University of Ottawa professor and former Trudeau foreign policy adviser. He learned. You can't do that.
Another thing buoying Trudeau has been the near-universal Canadian response to Trump's comments.
After Trudeau's news conference, Trump pulled the USA out of the G-7's official statement of common values and accused the prime minister, who hosted the G-7 conference, of making "false statements" while also blasting him as "very dishonest and weak".
Trump also continued to denounce Canada's system of supply management to protect the domestic dairy, egg and poultry industry, which levels tariffs of up to 300 per cent on American imports of those products.
If the US imposes a 25 per cent tariff on those exports, suddenly they don't make much economic sense, said Kristin Dziczek, vice president of industry, labour and economics at the Center for Automotive Research in Ann Arbor, Mich.
"From the beginning we have said that our approach would be to work for the best possible outcome but to always be prepared for the worst, to have backup plans", she said.
"Sometimes when we think about tariffs, when we think about a trade war, we lose sight of the real impact, and that's on workers", Singh told a news conference.