Trump's looming summit with North Korean leader Kim Jong Un heightened tension, and White House economic adviser Larry Kudlow accused Trudeau of betraying Trump with "polarizing" statements on trade policy that risked making the USA leader look weak on the eve of the historic North Korea summit.
Trump said he chose to back out of the G7 communique after watching Trudeau's closing summit news conference, at which he warned that Canada would not be pushed around on tariffs - a point the Canadian prime minister had made several times before.
Subsequently, Trump said he had instructed his representatives not to endorse a joint communique put out by the Group of Seven leaders after what he called Trudeau's "false statements" at a news conference.
Theresa May drew roars of laughter from MPs after she was asked to chose between Canadian leader Justin Trudeau and US President Donald Trump.
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Without any resolution, Trudeau has promised to impose retaliatory tariffs on metals and a range of other USA products by Canada Day.
Trump, who had criticised Trudeau after the G7 meeting in Canada on the weekend, said the United States had a big trade deficit with Canada, and "a little balance" was needed.
Conservative House Leader Candice Bergen says her party is united with the Liberals when it comes to defending Canada's trade interests. Larry Kudlow, the president's economic adviser, finished the pile-on by accusing Trudeau of "betrayal", while Trump's new trade adviser, Peter Navarro, said later on Fox News Sunday that Trudeau is a back-stabber who "engaged in bad faith" and deserves a special place in hell. He added, "Canadians, we're polite, we're reasonable, but we also will not be pushed around".
The outburst against Trudeau, and by association the other G7 members, is only the latest incident in which Trump has clashed with America's closest allies, even as he has had warm words for autocrats like Kim and Russia's Vladimir Putin. Trump imposed steep tariffs on steel and aluminum last month to rebalance trade, he said.
"Justin acts hurt when called out!" the USA president said in his latest Tweet.
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Ten per cent of the Canadian dairy market is open to imports, with the rest effectively blocked by massive tariffs. "I don't know what it might be, but the message that the president sent was so strong to one of our allies that I really don't understand why they would do that unless he truly felt that there had been a violation of trust".
Canada is America's largest trading partner, he said, adding that the US economy would struggle to make up for Canada's absence in a tariff tit-for-tat. "We just shook hands!"
"We are convinced that a modernisation is perfectly possible, we are convinced that common sense will triumph", she said. "It was very friendly", Trump said.
In a statement Monday, British Prime Minister Theresa May said: "I want to pay a particular tribute to Prime Minister Trudeau for his leadership and skillful chairing".
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Kim smiled as he took a selfie with Singapore's Foreign Minister Vivian Balakrishnan at the scenic waterfront Gardens by the Bay. Mr Lee, it said, complimented "the bold and admirable decision" by Mr Kim and Mr Trump to come together for the summit.