Trump's change of heart appeared to have been invoked by Trudeau's comments on Trump's steel and aluminum tariffs against Canada and other allies. "Our Tariffs are in response to his of 270% on dairy!" he added.
"It's very unfair to our farmers".
Trump claimed America had been obliged to levy the metals tariffs as it has been exploited as the world's "piggy bank" under existing arrangements, but his counterparts were equally determined to protect "rules-based" worldwide trade. You can't do that.
"Tariffs are going to come way down because we people can not continue to do that".
"I congratulate leaders of other countries for so crazily being able to make these trade deals so good for their countries", Trump said, while insisting that his relationships with Europe and Canada were "outstanding".
Trudeau said he had reiterated to Trump that tariffs would harm industries and workers on both sides of the U.S.
At a news conference held in Charlevoix, Canada, Trudeau announced that all seven countries in the summit had agreed on "a joint communique". "He was the one who let Crimea get away - that was during his administration", he said, adding: "Obama can say all he wants, but he allowed Russian Federation to take Crimea".
Meanwhile, the European Union - the world's largest trading bloc - announced last week it would impose retaliatory tariffs on the USA beginning in July, over Washington's duties on steel and aluminum imports from Europe. All three trading partners have threatened to retaliate with their own levies against US imports.
"We'll win that war 1,000 times out of a 1,000", he said.
The war of words between Trudeau and Trump escalated after the USA president left the meeting early. "I don't blame other leaders for that, I blame our past leaders".
Instead of fighting big battles, his counterparts were angling for a baseline of agreement that might be as low as an acknowledgement of the important role of the G-7. US negotiators have frequently sparred with Mexican authorities over wages and workers' rights.
The joint communique that was thrashed out over two days of negotiations vowed that members would reform multilateral oversight through the World Trade Organization (WTO) and seek to cut tariffs.
The President said Canada and Mexico were also close to a deal on a sunset clause on NAFTA, but a senior Canadian official said Ottawa is not interested in such a clause that would trigger reopening the trade pact in five years. "While sending their product into our country tax free", he said.
Yet, his threat to not sign the Communique also has the potential to upend, not only his gains with Trudeau and Canada, but a lot of the goodwill gained by the conference.
President Donald Trump's planned meeting with French President Emmanuel Macron at the G7 is being pushed back to late Friday afternoon after a delayed departure from the White House.