Bruce Heyman, who served as ambassador from 2014 to 2017, gave Canada a "tsunami warning," saying if Trump takes the White House, Canada is at great risk.

Heyman's warning came on the sidelines of the Democratic National Convention, where thousands of party faithful have gathered to rally behind Kamala Harris and bask in the excitement building around the vice-president since she quickly ascended to the top of the ticket.

The enthusiasm, while palpable in the halls of the convention, does not guarantee a win in November and Heyman says it critical that Americans around the world ensure their vote counts.

He says there are at least 6.5 million eligible voters living in other countries, mainly in Canada and Mexico.

When President Joe Biden was elected in 2020, Heyman says votes from Americans abroad played a key role in clinching battleground states.

Heyman said much of that support was shored up through a website and outreach targeting American voters from abroad.

Those efforts resulted in the amount of votes from Americans elsewhere in the world increasing by more than 73 per cent in 2016, and half of those votes went to battleground states.

"Americans in Canada, you can be part of the decision of who wins the election in the United States," Heyman said on Wednesday.

Harris is set to officially accept the party's nomination Thursday and deliver a speech that will formally introduce her as the Democrats' pick for president. The day's theme is "For our Future."

The former ambassador said the election could prove critical for the future of Canadians, too. Heyman, who was appointed under former president Barack Obama, became well known for strengthening the relationship between Canada and the U.S. under both former prime minister Stephen Harper and Prime Minister Justin Trudeau.

Heyman and his wife, Vicki, left as Trump took America's reins but remained connected to Canada, even writing a book about their experiences with Canadian diplomacy. They since have supported Democratic campaigns.

The first Trump administration proved tumultuous for Canada, he said, with the former president's policies affecting more than trade.

Thousands of people in the U.S., afraid of rumours of deportation, started travelling into Canada outside of regular border crossings.

Trump has promised to deport 11 million undocumented immigrants if he gets a second term. Heyman said he believes that people, once again motivated by fear, would start to flee north in even higher numbers.

"I don't believe Canada is prepared for those kinds of numbers to come across the border," he said.

If bans against abortion expand further in the U.S., Heyman forewarned, people may look to Canada for help. If Trump claws back environmental policies, it could affect Canada's investment into green technologies, Heyman said.

And if a Trump administration removes support from NATO and other alliances, Canada's stature around the world would diminish alongside the U.S., Heyman said.

He added that Canada would likely have to fast-track its NATO defence funding commitments to avoid Trump's wrath. Trudeau said last month that Canada expects to hit its target of two per cent of national gross domestic product on defence by 2032.

The Republican party's platform hints at further protectionist policies, and Trump has signalled plans for a 10 per cent tariff on imports.

"I think that for Canada, it's a high risk -- the Trump administration -- if he implements the policies he says he wants to implement," Heyman said.

"And the greatest risk for Canada is he does it all at once as ... swarm tactic to attack Democrats."

This report by The Canadian Press was first published Aug. 22, 2024.