Former prime minister Brian Mulroney said today weekend attacks on Prime Minister Justin Trudeau by surrogates of U.S. President Donald Trump were unprecedented — but Canadian negotiators shouldn't let the remarks throw them off their trade strategy.

Mulroney — who was prime minister when both the original Canada-U.S. Free Trade Agreement and the North American Free Trade Agreement were negotiated — said the Canadian side must not let static from the White House distract from the more serious business of managing the trade relationship with the U.S. and completing high-stakes negotiations on a new NAFTA accord.

"I've never seen language like this. Least of all from subordinates of the president directed at the prime minister of their greatest friend and ally," he said. "This, I've never seen before. Nor has anybody else."

Mulroney also said Trudeau's words in the closing hours of the G7 summit in Charlevoix, Que. — the ones that seemed to have sent the president into a rage — were hardly unexpected.

"All Mr. Trudeau was doing was, in a rather gentle way, articulating the position of his government, which would be the position of any Canadian government in these circumstances," he said.

"So I don't view it as lethal.... International negotiations, they have their ebbs and flows. This is an ebb."

The former PM said Trudeau would be wise to steer clear of engaging in a Twitter brawl with the president, and added the government's plan to impose retaliatory tariffs on U.S. products is a sensible response.

"Somebody puts a tariff on your products, you put a tariff on theirs. Now, how it's received on the other side is something else — but that's life."

Canada-U.S. relations seemed to have reached their lowest point in more than a generation after Trump tweeted Saturday that he was withdrawing support from a G7 joint communique, while complaining he had been blindsided by Trudeau's criticism of U.S. tariffs at a closing G7 news conference.

As he flew from Canada to Singapore Saturday night, Trump took to Twitter to label Trudeau "dishonest" and "weak."

Trump's advisers piled on over the weekend, with White House trade adviser Peter Navarro telling Fox News that "there's a special place in hell" for Trudeau. Trump's economic adviser, Larry Kudlow, suggested Trudeau's comments somehow made the president look weak on the eve of a summit meeting with North Korean dictator Kim Jong-un.

"POTUS is not going to let a Canadian prime minister push him around … on the eve of this," Kudlow said. "Kim must not see American weakness."

Mulroney said he pointed out to U.S. Commerce Secretary Wilbur Ross that Trump is complaining of flawed trade deals at a time when the U.S. economy is running white hot.

"I said to him, 'Wilbur, If I had a 3.8 per cent unemployment rate. I'd still be prime minister of Canada."

He suggested that Trudeau hold off on attempting any personal diplomacy with Trump until after the North Korea summit.

"If (Trump) does well in Singapore, that will take this thing off the front pages and the president will feel happy with himself."