Andrew Cohen is an author and journalist who writes a nationally syndicated column for the Ottawa Citizen. His latest book is "Two Days in June: John F. Kennedy and the 48 Hours that Made History" (Signal/Random House). He is a Global Fellow at the Woodrow Wilson International Center in Washington. The opinions expressed in this commentary are solely those of the author.

Ottawa, Canada (CNN) In one bizarre, unguarded moment at a private fundraiser in Missouri, Donald Trump showed why months of trade negotiations between Canada, Mexico and the United States have been fitful, frustrating, and fruitless.

Andrew Cohen

In an earlier conversation with Prime Minister Justin Trudeau, the President made up facts about the balance of trade with Canada -- and later boasted about it. On Wednesday, he told donors that he had claimed, falsely, that the United States has a trade deficit with Canada. On Thursday, he repeated the canard.

In fact, when the Washington Post published a transcript of the conversation, Trump tweeted "we do have a Trade Deficit with Canada, as we do with almost all countries (some of them massive). P.M. Justin Trudeau ... doesn't like saying that Canada has a Surplus vs. the U.S. (negotiating), but they do ... they almost all do ... and that's how I know!"

And that's how I know.

To Canada, Trump's braggadocio, ignorance and self-confidence are no surprise. After a year of dealing with Trump -- in meetings at the White House, over the telephone, and across the table from US negotiators re-opening NAFTA -- Trudeau is used to Trump's hyperbole and inconsistency and even this, the most brazen of his falsehoods.