President Donald Trump and Canadian Prime Minister Justin Trudeau participate in the family photo during the G-7 Summit in Charlevoix, Canada.

QUEBEC CITY — Bashing the leader of one of America’s venerable allies, the White House escalated its trade tirade and leveled more withering and unprecedented criticism Sunday against Canada’s prime minister, branding Justin Trudeau a back-stabber unworthy of President Donald Trump’s time.

“There’s a special place in hell for any foreign leader that engages in bad faith diplomacy with President Donald J. Trump and then tries to stab him in the back on the way out the door,” Trump trade adviser Peter Navarro said in an interview nationally broadcast in the U.S.

The verbal volleys by Navarro and Trump’s top economic adviser, Larry Kudlow, picked up where Trump left off Saturday evening with a series of tweets from Air Force One en route to Singapore for his nuclear summit Tuesday with North Korea’s Kim Jong Un.

Just as the Trudeau-hosted Group of Seven meeting of the world’s leading industrialized nations had seemed to weather Trump’s threats of a trade war, the president backed out of the group’s joint statement that Trudeau said all the leaders had come together to sign. Trump called Trudeau “dishonest & weak” after Trudeau said at a news conference that Canada would retaliate for new U.S. tariffs.

Trudeau didn’t respond to questions about Trump when the prime minister arrived at a Quebec City hotel Sunday for meetings with other world leaders. A Trudeau spokesman, Cameron Ahmad, said Saturday night that Trudeau “said nothing he hasn’t said before — both in public and in private conversations” with Trump.

And Roland Paris, a former foreign policy adviser to Trudeau, jabbed on Trump on Twitter: “Big tough guy once he’s back on his airplane. Can’t do it in person. ... He’s a pathetic little man-child.”

Trudeau said he had reiterated to Trump, who left the G-7 meeting before it ended, that tariffs would harm industries and workers on both sides of the U.S.-Canada border. Trudeau told reporters that imposing retaliatory measures “is not something I relish doing” but that he wouldn’t hesitate to do so because “I will always protect Canadian workers and Canadian interests.”

Navarro, the Trump trade adviser, said his harsh assessment of what “bad faith” Trudeau did with “that stunt press conference” on Saturday “comes right from Air Force One.”

He said Trump “did the courtesy to Justin Trudeau to travel up to Quebec for that summit. He had other things, bigger things, on his plate in Singapore. ... He did him a favor and he was even willing to sign that socialist communique. And what did Trudeau do as soon as the plane took off from Canadian airspace? Trudeau stuck our president in the back. That will not stand.”

Kudlow, in a separate TV appearance, said Trudeau was “polarizing” and “really kind of stabbed us in the back.” The Canadian leader pulled a “sophomoric political stunt for domestic consumption,” Kudlow said, that amounted to “a betrayal.”

“Don’t blame Trump. It was Trudeau who started blasting Trump after he left, after the deals had been made.”

Trudeau had said Canadians “are polite, we’re reasonable, but also we will not be pushed around.” He described all seven leaders coming together to sign the joint declaration despite having “some strong, firm conversations on trade, and specifically on American tariffs.”