opinion
Open this photo in gallery:

Prime Minister Mark Carney speaks with U.S. President Donald Trump at a working lunch with leaders of G7 and the Middle East in Evian-les-Bains, France on June 16.Evelyn Hockstein/The Associated Press

In 1962, when Charles De Gaulle was offered photographs proving the Soviet Union was stationing nuclear missiles in Cuba, the French president waved the photographs away. “The word of the President of the United States is good enough for me,” he reportedly said.

This is what Donald Trump has squandered.

There was a time when an American president could be taken at his word. Yes, there were exceptions: Richard Nixon declaring he knew nothing about the Watergate burglary; George W. Bush insisting Iraq under President Saddam Hussein had produced chemical weapons.

And presidents have made promises that Congress has failed to keep, from the Senate refusing to endorse the Woodrow Wilson’s commitment to join the League of Nations in 1920 to Congress this year failing to pass legislation backed by Mr. Trump that would restrict voting rights.

The full list of Canadian goods targeted by Trump’s new 50% tariffs, and what Canada is doing about it

But this president has gone where no U.S. president has gone before. He has repudiated the commitments of previous presidents and Congresses, repudiated his own previous commitments, and sometimes repudiated those repudiations, rendering not just his word but the word of the government of the United States virtually without worth.

This leaves Prime Minister Carney and his advisers in an impossible situation. The Americans are demanding concessions from Canada beyond those already offered as a precondition for talks to revise and renew the Canada-United States-Mexico trade agreement.

But why on earth would the Canadian government offer concessions on CUSMA, knowing that any future agreement could be tossed aside the next time Mr. Trump gets into a snit?

Over and over again, this president has demonstrated that his word, not to mention existing treaties, is anything but binding. He has repeatedly questioned America’s commitment to NATO, first on the grounds that other members don’t spend enough on defence, and more recently because they refused to come to America’s aid when it attacked Iran.

European nations are racing to build up defences against a possible Russian attack in Eastern Europe, knowing they can no longer count on the United States having their back.

Playing defence didn’t protect Canada from Trump’s latest tariffs. It’s time to move into the offensive zone

The Trump administration has at various times cut off, and then restored, American support for Ukraine in the wake of the Russian invasion. He has imposed, lifted and reimposed tariffs on nations around the world.

No country has suffered more from tariff impositions and shifts than Canada. This country endures tariffs on steel, aluminium and automobiles, and faces a fresh batch of targeted tariffs – some of which would violate CUSMA – that will come into effect Aug. 19 unless a new agreement is reached.

On top of all this, the U.S. President is threatening to impose tariffs to punish Canada for wildfire smoke that has drifted into the United States this summer.

And then there is the infamous case of the Gordie Howe Bridge connecting Windsor to Detroit. Canada paid for the bridge and agreed to share revenues with Michigan, after construction costs had been recouped. But then Mr. Trump horned in, demanding that the U.S. government receive a cut. Ottawa swallowed hard and agreed to give the United States a piece of the action.

How do Canada and its allies get by in a world in which the United States, despite remaining vibrant economically and culturally, has become so politically dysfunctional that a plurality of voters elected a president who repeatedly muses about annexing Canada and turning this country into the 51st state? Who wants to annex Greenland, despite the fierce opposition of Greenlanders and Danes?

It is true that Mr. Trump’s term runs out in two and a half years, and that the next U.S. president may try to assure allies that the United States can once again be trusted as a responsible partner. But the world knows that America is always one election away from another MAGA White House. No deal signed with the United States is a secure deal.

This must be terrifying to people in Poland and the Baltic States and South Korea and Taiwan, knowing that their American ally can no longer be trusted to come to their aid if they face invasion.

Charles De Gaulle and many other world leaders over decades assumed as a matter of course that an American president’s word was his bond. That is no longer true, making the world a more dangerous place.

Follow related authors and topics

Authors and topics you follow will be added to your personal news feed in Following.

Interact with The Globe