WASHINGTON — President Trump repeated on Thursday his false assertion that the United States runs a trade deficit with Canada, the morning after privately telling Republican donors that he had deliberately insisted on that claim in a meeting with Prime Minister Justin Trudeau of Canada without knowing whether it was true.

Mr. Trump’s private admission to having a loose grasp of the facts and his public refusal to back down from the incorrect statement — the United States has an overall surplus in trade with Canada — were vivid illustrations of the president’s cavalier attitude about the truth, and a reminder of how that approach has taken hold at the White House.

Sarah Huckabee Sanders, the White House press secretary, said Mr. Trump had chosen his figures selectively in the conversation with Mr. Trudeau and in a subsequent Twitter post that repeated the claim. The president was referring only to the trade of goods, Ms. Sanders said, which ignores the larger trade surplus in services the United States exports to Canada.

And in a briefing with reporters, she acknowledged that Mr. Trump had fabricated an anecdote he told the donors about unfair trading practices — Japanese officials, he claimed, conduct a test on American cars by dropping a bowling ball on their hoods from 20 feet high, and those that dent are barred from being imported.