Speaking at the Wall Street Journal CFO Network annual meeting in Washington, Navarro said he used language that was "inappropriate". "I own that; that was my mistake, my words".
Republican Senate Finance Chairman Orrin Hatch said the comment was "out of line", telling Politico the adviser "should have kept his big mouth shut because I don't think that helps us in foreign policy".
"Very childish and unprofessional behaviour", Gorka said.
What was new was Trudeau's news conference Saturday, where he said that Canadians "will not be pushed around" and added that the Trump administration's national security justification for imposing tariffs on steel and aluminum imported from Canada is "kind of insulting". "We just shook hands!'" Trump said Tuesday.
It seems the true explanation for Trump's rhetorical attack on Trudeau is not Canadian tariffs or the content of the prime minister's news conference.
The communique - which had appeared to have papered over the cracks that surfaced at the summit - said the leaders of the US, Canada, Britain, France, Italy, Germany and Japan agreed on the need for "free, fair, and mutually beneficial trade" and the importance of fighting protectionism.
Trump fired off a volley of tweets on Monday further venting anger at North Atlantic Treaty Organisation allies, the European Union and Trudeau.
Both aides accused Trudeau of betraying Trump when he gave a news conference after the USA president had departed. And that's what bad-faith Justin Trudeau did with that stunt press conference.
Navarro came under scrutiny Sunday for bashing Trudeau after the prime minister criticized Trump in the wake of the G-7 summit held in Canada. He said that Canada has to stand up for itself.
"There are more jobs now posted than there are people looking for work in the United States, and we've cut immigration pretty substantially", he said, noting that the country's birth rate is low.
On Monday, MPs in the House of Commons approved a motion denouncing Trump's name-calling tirade and endorsing Trudeau's decision to stand his ground against US tariffs and tweeted presidential threats. And I'll tell you this: "To my friends in Canada, that was one of the worst political miscalculations of a Canadian leader in modern Canadian history". The fight also seriously raises the likelihood that the current round of tariffs could escalate into a full-blown trade war.