Shortly before Canadian Prime Minister Mark Carney arrived at the White House, Donald Trump published an unambiguously hostile message to his social media platform, setting the stage for a meeting that could’ve quickly descended into disaster.

Fortunately for everyone involved, that didn’t happen. There were contentious moments: Carney told Trump that his country is “not for sale,” becoming the latest in a series of foreign leaders to rebuff the American president to his face; and there was a confusing moment when Trump appeared confused about the meaning of the word “concession.” But in general, the Republican was unexpectedly civil toward his Canadian counterpart.

Those fearing a replay of Trump’s ugly Oval Office meeting with Ukrainian President Volodymyr Zelenskyy from February had reason to be relieved.

But one brief exchange did stand out for me.

The Republican president, apparently eager to explain why Canada should become an American state, said of the border between the two countries, “When you get rid of that artificially drawn line — somebody drew that line many years ago with like with a ruler, just a straight line right across the top of the country — when you look at that beautiful formation, when it’s together — I’m a very artistic person — but when I looked at that beaut, I said, ‘That’s the way it was meant to be.’”

Not surprisingly, this did not prove persuasive, and Carney did not appear altogether pleased with the comment. What stood out for me, however, was the familiarity of Trump’s rhetoric.

In January, for example, a couple of weeks before his second inaugural, Trump endorsed getting rid of “that artificially drawn line” between the United States and Canada. In mid-March, after hosting an infomercial on the White House South Lawn for his biggest campaign donor, the president again set aside some time to pontificate on the border separating the two countries, describing the dividing line as “artificial.”

A day later, as NBC News reported, Trump held an Oval Office event alongside NATO Secretary General Mark Rutte and again told reporters that he sees the border between the U.S. and Canada as “an artificial line,” adding, “Somebody did it a long time ago, many, many decades ago, and [it] makes no sense.” In late March, Trump again complained about “that artificial line.”

In each instance, including the Oval Office meeting with Carney, the president brought this up on his own. It’s not as if reporters asked Trump to share his thoughts on the subject, prompting him to reflect. Rather, despite years of emphasis on the integrity of territorial boundaries, he just keeps blurting this out.

The question, of course, is why.

As we’ve discussed, for all intents and purposes, Trump’s modern political career began when he came down a golden escalator nearly a decade ago. In the years that followed, he never expressed much interest in the dividing line between his country and our neighbors to the north.

He didn’t talk about this at rallies; he didn’t publish tweets about it; he didn’t air ads about it; he didn’t invest any energy into this during his entire first term; and he certainly never told voters in any of his three national races that he’d make this a priority.

What’s more, it’s not as if there’s a sizable group of voters who are demanding revisions to the 1908 border treaty.

And yet Trump keeps bringing this up, suggesting he considers the claim important.

I still have no idea who put this thought in his head, though it’s worth noting for context that there is another prominent international figure who routinely references an “artificial” line between his country and his neighbor: Vladimir Putin has used the same rhetoric in recent years to describe the border between Russia and Ukraine.

This post updates our related earlier coverage.