The other six G7 nations reiterated their support for the Paris agreement on climate change and acknowledged they would have to continue their fight without the U.S.
Larry Kudlow said Mr. Trump negotiated in good faith with fellow global powers in Quebec.
On June 1, the USA imposed a 25 per cent tariff for steel and 10 per cent for aluminium on imports from the European Union (EU), Canada, and Mexico.
"This too shall pass", tweeted the former Federal Bureau of Investigation director, who referred to Trump as a "mafia boss" in his recent tell-all, "A Higher Loyalty".
"President Donald Trump's White House physical states he is 6'3", however it appears that while he is standing next to Canadian Prime Minister Justin Trudeau, that number might be a stretch. But the Canadian prime minister's post-conference criticism Saturday was "a betrayal" that required a response from Trump, to avoid showing weakness on the eve of talks with North Korean leader Kim Jong Un, he added.
"We need to stand with our democratic allies", Feinstein said.
A senior U.S. administration official said that Mr Trump had been angered by Mr Trudeau's comments.
In response, Canada, Mexico and the European Union said they were putting in place their own retaliatory measures.
A French presidential official, speaking on the condition of anonymity, said that after two days of trying to gain commitments and consensus, all of Europe was sticking to the agreed document.
He blamed the summit's host: Prime Minister Justin Trudeau.
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Yet after leaving the summit, Mr Trump tweeted that he would instruct U.S. officials not to endorse the G7 statement, after objecting to comments from summit host Mr Trudeau.
"Canadians are polite and reasonable but we will also not be pushed around", he said.
He said the move was based on Mr Trudeau's "false statements. and the fact that Canada is charging massive tariffs to our U.S. farmers, workers and companies".
"PM Justin Trudeau of Canada acted so meek and mild during our @G7 meetings only to give a news conference after I left saying that, "US Tariffs were kind of insulting" and he "will not be pushed around". May is not only hoping that Trump lift new tariffs on European aluminium and steel, but that he will promise a favourable pro-Brexit trade deal with the United Kingdom after it leaves the European bloc.
Navarro, Trump's top trade adviser, in an appearance on Fox News, declared Trudeau's comments "one of the worst political miscalculations of a Canadian leader in modern Canadian history". Earlier this week, Merkel said the group is defined by its members' respect of worldwide law, and Russia's 2014 annexation of Crimea was a "flagrant breach" of that.
He instructed US representatives not to sign the communique from the summit, raising new questions about Mr. Trump's strained relationship with leaders of historic allies.
"They should have said to him, 'God speed, you are negotiating with the insane nuclear tyrant in North Korea, and we are behind you, '" Kudlow added.
Trump lashed out at Trudeau after the G7 issued a fragile joint communique in which the embattled alliance managed to overcome some differences and find areas of common ground.
Canada's foreign minister, Chrystia Freeland, said her country "does not conduct its diplomacy through ad hominem attacks".