No doubt you've already heard about the baleful impact a Trump presidency would have on the Canadian economy. The Republican presidential nominee's threat to tear up the North American free-trade agreement, while aimed at Mexico, could sideswipe this country too. His anti-free-trade agenda, especially his threat to impose tariffs on Chinese imports, could lead to a trade war and a global recession that would be particularly devastating for Canada, which is so reliant on trade.

But with Donald Trump now essentially tied with Democratic rival Hillary Clinton in the polls, it's time to examine some other ways a Trump presidency would resonate in Canada.

As it turns out, the deeper you dive, the darker it gets.

Story continues below advertisement

NORAD in the cross hairs: Mr. Trump is threatening to withdraw the American security umbrella from Japan and South Korea. He has warned NATO allies that the United States might renege on the treaty if they don't pay up. Canada should therefore expect demands from a President Trump for a more robust contribution to NORAD if this country wants to remain a full partner in continental air defence.

America votes: Coverage of the 2016 U.S. election night

Related: Trump's win, Canada's loss: Imagining a NAFTA-free future

Read more: How a Trump presidency would affect Canada's economy

Giving up on fighting climate change: If Donald Trump is elected president the Liberals might as well shut down their plans to ratify the Paris Agreement on Climate Change. They will also have to abandon plans to introduce a carbon price. Mr. Trump believes global warming is a hoax perpetrated by the Chinese to hobble American industry. He has promised to scrap Democratic actions to lower carbon emissions and has said he will repudiate the Paris Agreement if elected. The global effort to fight climate change will be dead in the water. Under the circumstances, unilateral Canadian action to combat global warming would be futile and not worth the economic cost.

Smog over Toronto: Restrictions on burning coal imposed by the Obama administration contributed to improved air quality in eastern North America. Mr. Trump wants to end those restrictions. "Regulations that shut down hundreds of coal-fired power plants and block the construction of new ones – how stupid is that?" he asked rhetorically back in May. With coal-fired plants once again running full tilt, and others under construction, we should expect a return to the bad old smog days in Ontario, as the Ohio Valley once again exports its pollution via prevailing winds.

An end to Canada's open door: Previous Republican administrations have grumbled that Canada lets in too many people without sufficient screening. President Trump would be certain to increase pressure on Canada to limit its intake of both immigrants and refugees, especially from Muslim regions, on pain of tighter border controls. To preserve whatever is left of access to the American market, the federal government might have no choice but to comply.

Story continues below advertisement

On the other hand, Canada would likely welcome more American immigrants than at any time since the draft dodgers fled the Vietnam war.

An end to Five Eyes: Mr. Trump says he doesn't trust the intelligence services, blaming them for failing to deter terrorist attacks. He promotes unconstitutional surveillance and detention of suspects. As a result, the close intelligence co-operation of The Five Eyes – U.S., U.K. Canada, Australia and New Zealand – would likely be disrupted. If the Americans didn't terminate the intelligence-sharing agreement, the other nations probably would.

The Canadian-American trade war: Buy America policies already prevent Canadian firms from bidding on U.S. infrastructure projects. Expect those proscriptions to expand under a President Trump. Expect the softwood lumber negotiations to go nowhere and the Americans to import punitive tariffs. Expect tariffs on other exports, as the protectionist Mr. Trump seeks to preserve American jobs by limiting foreign, including Canadian, competition. The tariffs will be illegal under WTO rules, but Mr. Trump has made it clear he plans to disregard those rules. As for Mr. Trump's vow to penalize companies that move jobs out of the country, he probably can't. But why would Ford take the risk of incurring the Trump administration's wrath by expanding operations in Canada?

The deepest chill in Canada-U.S. relations since the War of 1812: Justin Trudeau is the antithesis of Donald Trump. Pro-trade, pro-immigration, pro-environment, popular as opposed to populist, post-national as opposed to nativist, there may be no head of government a President Trump would take to less. On top of all of the problems listed above, neither man would like the other in the least. Neither would have the least desire to be photographed in the other's office. Canada's closest ally and trading partner would become a stranger at best, and an antagonist at worst.

On the other hand...: Donald Trump is a big supporter of the pipeline that would send Alberta bitumen to Gulf refineries. This would be good news for the oil sands, but cold comfort in a world reeling from the chaos of a Donald Trump presidency.