President Trump is nothing if not strong-willed, and he’s the leader of the mightiest nation on Earth — but there’s one power even Mr. Trump can’t afford to discount.

It’s the power of nationalism and national pride, which Trump himself harnessed to win two terms in the White House.

Yet the same force that helped make Mr. Trump president will wreck his presidency if he fails to take it seriously enough in his foreign policy.

Mr. Trump is a consummate dealmaker, and bargaining with friends and foes alike depends on appealing to their self-interests.

Yet self-interest isn’t always a stronger motive than self-respect where other nations are concerned.

The president could get away with needling Prime Minister Trudeau, referring to him as the “governor” of Canada.

Yet he can’t tease Canada into becoming America’s 51st state, and outright economic warfare — if the threatened tariffs ever come into full effect — won’t suffice either. 

Mr. Trump demolished Mr. Trudeau’s premiership, but the American president is actually strengthening Canada’s Liberal Party, whose new leader, Mark Carney, has called snap elections to capitalize on the opportunity Mr. Trump has created for him.

Canadians were dismayed by Mr. Trudeau’s Biden-like performance and ready to dump the Liberals in favor of the Conservative Party and its leader, Pierre Poilievre. 

The Conservatives had a wide lead in polls — until Trump declared a trade war and started talking about taking over Canada.

Canadians know full well how dependent they are on American trade, but they also feel there’s more than money at stake here: Mr. Trump has called into question Canada’s very right to exist as an independent nation, and that’s awakened Canadians’ long-dormant nationalism.

Mr. Carney, as leader of the party in power in Ottawa, gets to play hero by promising to stand up to the foreign bully, and now polls show the Liberals tied with the Conservatives — who have been quick to assert their own patriotic zeal in condemning Trump’s policies.

Appearing on Fox News’ “The Ingraham Angle,” Mr. Trump professed not to care about who won the Canadian election and even said, “I’d rather deal with a liberal than a conservative.”

Was that a bit of reverse psychology to turn Canada’s fury at Mr. Trump against the Liberals?

Or does Mr. Trump think a few more years of Liberal government will cripple Canada and make his offer of union with America more attractive? 

Either way, he’s playing with fire — nationalism isn’t easily quenched once it gets going, and Canadian national identity has for 250 years been defined by not being American.

It’s the land America’s pro-British Tories fled to during our Revolutionary War, after all.

Canadians and Americans might look and sound a lot alike, but then the same can be said about Ukrainians and Russians. 

Mr. Trump’s disregard for Canadian nationalism risks turning our closest ally, geographically speaking, into a suspicious neighbor.

Ironically, Mr. Trump is in his own way paying Canada a high compliment — he knows real estate, and he sees Canada as immensely valuable for the United States. 

Yet the Canadians aren’t looking to sell at any price.

Denmark, likewise, isn’t looking to sell Greenland, although doing so wouldn’t mean the end of Denmark as its own country.

The Greenlanders themselves have thought about independence, though their population and economy are so small that controlling the world’s largest island on their own — at a time when the Arctic is of rising economic and military importance — isn’t very practical.

Yet what will Trump do if the Danes or the Greenlanders, or both, don’t want a deal?

Panamanian nationalism is tightly tied to the Panama Canal, and while the government may not be able to hold out against American pressure, the people of that land would find surrender of the canal to American ownership a bitter thing to swallow.

The Trump administration is wise to think in terms of the Monroe Doctrine and the security of America’s own hemispheric neighborhood.

Yet a heavy-handed approach that aligns nationalism with anti-Americanism from the Yukon to the Caribbean would be disastrously counterproductive. 

The more America acts like an imperial power, the more nationalist movements in other countries will treat us like one.

In the Cold War, the Soviet Union was surprised to discover neither tanks nor secret police could extinguish a yearning for independence and freedom in the captive nations of Eastern Europe.

Unfortunately, where communists did use nationalism and anti-imperialism to their advantage — in Southeast Asia and elsewhere in the Third World — they often succeeded.

Vladimir Putin’s Russia is less powerful but far more intimidating than America, yet Mr. Putin too was shocked to find Ukraine would not submit to threats or force.

Mr. Trump is a proud American patriot, which is one reason he dreams of expanding the nation’s territory.

To succeed in diplomacy and grand strategy, though, Mr. Trump will have to make nationalism work for him, not against him, just as he did in domestic politics.

Creators.com