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 today 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. Kudlow suggested Trump saw Trudeau as trying to weaken his hand before that meeting, saying the president won’t “let a Canadian prime minister push him around. … Kim must not see American weakness.”

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 today 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.” Kudlow said Trump won’t let people “take pot shots at him” and that Trudeau “should’ve known better.”

But the criticism left a former Canadian prime minister, Stephen Harper, stumped. “I don’t understand the obsession with trade relations with Canada,” he said, given that Canada is the biggest single buyer of American goods and services in the world. From promoting democracy and to fighting terrorism, “we’re on the same page. We’re the closest partners in the world and you don’t want to see a dispute over one particular issue poison everything.”

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.”

In the air by then, Trump tweeted: “Based on Justin’s false statements at his news conference, and the fact that Canada is charging massive Tariffs to our U.S. farmers, workers and companies, I have instructed our U.S. Reps not to endorse the Communique as we look at Tariffs on automobiles flooding the U.S. Market!”

He followed up by tweeting: “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.” Very dishonest & weak. Our Tariffs are in response to his of 270% on dairy!”

Before leaving for Singapore, Trump had delivered a stark warning to America’s trading partners not to counter his decision to impose tariffs on steel and aluminum imports. The G-7 also includes Britain, Italy, France, Germany and Japan.

“If they retaliate, they’re making a mistake,” Trump said.

Trump insisted relationships with allies were a “10” just before he left the summit.

At a rare solo news conference before heading to Asia, Trump said he pressed for the G-7 countries to eliminate all tariffs, trade barriers and subsidies in their trading practices. He reiterated his longstanding view that the U.S. has been taken advantage of in global trade, adding, “We’re like the piggy bank that everybody’s robbing, and that ends.”

Navarro appeared on “Fox News Sunday,” and Kudlow was on CNN’s “State of the Union” and CBS’ “Face the Nation” and Harper spoke on Fox’s “Sunday Morning Futures.”