A familiar U.S. face finally showed up front and centre Saturday on the federal campaign trail: Donald Trump.

NDP Leader Jagmeet Singh promised to go toe-to-toe with the mercurial, unpredictable American president just as Justin Trudeau's Liberals released a new English-language ad touting their own record in confronting the White House during last year's tension-fraught free trade talks.

Trump served as a convenient political foil for the New Democrats in particular as both they and the Liberals battled for working-class votes on the first Saturday of the campaign — a day party caravans typically use to pause, refresh and reset their efforts for the coming week.

Singh vowed never to let Trump put the brakes on his plans to jump-start Canada's stalled auto sector and get manufacturing workers back on the job.

"You fight a guy like that — you just don't back up, you don't back down," he said during a campaign stop in Oshawa, Ont.

"When it comes down to it, just because he wants to create jobs in the United States doesn't mean we should give up on jobs in Canada. And we're not going to give up on jobs in Canada."

The Liberals also happened to be thinking about unions and blue-collar workers Saturday, unveiling "Fought Tooth and Nail" — a radio and internet ad, narrated by Chrystia Freeland, that celebrates the new North American trade pact and the successful end of punitive U.S. tariffs on Canadian aluminum and steel.

Trudeau, who spent the day shaking hands with members of the public throughout Quebec, including at a western festival and a local Tim Hortons, has been under sustained criticism from Singh and Conservative Leader Andrew Scheer over how the Liberal government handled the marathon talks, which lasted nearly a year and a half.

During that time — and the preceding months, when Trump seemed to delight in bashing NAFTA at every turn — Trudeau and Freeland were careful to avoid referencing the U.S. president by name. They instead referred generally to the American administration, a strategy government officials believed would avoid provoking Trump into drastic action that would threaten the effort.

But that strategy goes through a partisan wood chipper in the English-only ad, which is being deployed across southwestern Ontario — a Canadian manufacturing heartland that had a lot at stake in the free-trade effort — but not in Quebec, where dairy farmers are decidedly less pleased with the deal.

"We stood up to Donald Trump on trade when the Conservatives wanted Canada to back down," Freeland says in the ad over a visual of Trump greeting Trudeau at the White House. "The Conservatives told us to take any deal we could get. Capitulation is not a negotiating strategy."

During Thursday's leaders' debate, Scheer took aim at an absent Trudeau, saying the Liberal leader signed a deal with the United States and Mexico that hurts Canada's economic interest by caving to White House demands. And Green party Leader Elizabeth May cited a famous vaudeville puppet act to illustrate what she considers the Conservative leader's affinity for the president.

"You will do what Trump wants," she railed. "He might as well be the ventriloquist and you're Charlie McCarthy."

"That's just false," Scheer replied. "I believe that we should not sign away our sovereignty on our foreign affairs, which is what Justin Trudeau did when he signed NAFTA and conceded a huge concession to the United States on future trade deals and future exports of certain Canadian products."

On Saturday, despite his best efforts to talk about the Liberal leader, Scheer found himself fending off questions about a star Conservative candidate running in an Ottawa suburb and some of her past comments about Quebec — as well as her relationship to a far-right political commentator banned from Facebook.

Justina McCaffrey, outed on social media by the Liberals, apologized for the comments and distanced herself from Faith Goldy. Scheer accused his rivals of trying to distract from Trudeau's record as prime minister.

But McCaffrey, who introduced her leader at the event in the suburb of Kanata, refused to talk to reporters when she was done, fleeing into a waiting car and driving off.

Trudeau, for his part, was in show-don't-tell mode Saturday, glad-handing with voters in three Quebec ridings Saturday. But those voters wanted to know about his personal opposition to Quebec's controversial secularism law, Bill 21, which could pose an electoral hurdle for the Liberal chances in Quebec.

Singh was the only of the major leaders to lay down a policy plank on Saturday, and he did it with his own brand of Trump-style protectionism: a suite of measures to keep auto jobs in the country and encourage new-car buyers to spend their money on built-in-Canada cars and trucks.

The measures, also intended to encourage Canadian consumers and businesses to opt for zero-emissions vehicles, are part of the climate-change strategy the NDP unveiled in May and that Singh brandished an event later in the day at a farmer's market in downtown Kingston, Ont.

There, Singh doubled down on his anti-Trump stance, calling out the president's immigration measures at the U.S.-Mexico border, where the detention of migrants and the separation of families has made headlines for months.

"He's done really disgusting things," Singh said.

"We've got to call out the treatment of families: babies being ripped from the arms of mothers — that's horrible. They're fellow human beings; they should not be treated that way. The fact that Mr. Trudeau has remained silent and has not called that out is really troubling. It's wrong. You've got to call out people who are doing these types of things. Canadians expect it, I'm willing to do it, I'm prepared to do it."

The Liberals responded with a statement from Sandra Pupatello, a former Ontario Liberal cabinet minister trying to win in a longtime NDP riding in the border town and automotive hub of Windsor, Ont. Pupatello said Singh's opposition to the "new NAFTA" was the "quickest way to eliminate every single auto job in Canada" by cutting access to the American market.

Meanwhile, Green party Leader Elizabeth May was back in her Vancouver Island riding to attend a fair before travelling to the mainland for an evening event with a local candidate. On Monday, she'll preside over the release of the party's campaign platform.

People's Party of Canada Leader Maxime Bernier was in his Quebec stronghold of Beauce, and was scheduled to be in the area again Sunday before a few days of campaigning in New Brunswick.

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