What’s behind Donald Trump’s musings about absorbing other countries into the U.S.?

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As Donald Trump marked Christmas less than a month before returning to the U.S. presidency, he spent much of the festive season repeatedly musing about annexing Canada, Greenland and the Panama Canal.

The exact aim of the U.S. president-elect’s repeated expansionist declarations on social media is not clear – whether they are trolling, tactical negotiating threats or a serious embrace of imperialist manifest destiny.

And so far, the responses have been notably bifurcated. While the Canadian government has chosen to laugh off the comments as a joke, the leaders of both Panama and Greenland have pushed back in earnest.

Whatever Mr. Trump’s purpose, his rhetoric is a seeming contradiction with the isolationist approach to foreign policy he largely adopted in his winning campaign last month.

Roland Paris, a former foreign policy adviser to Prime Minister Justin Trudeau, said Mr. Trump’s talk does, however, appear to line up with his embrace of a bygone era in U.S. history: the president-elect has often praised the heavily protectionist economy of the late 1800s and early 1900s Gilded Age. His annexation ideation is similarly a throwback to long-ago U.S. dreams of continental territorial expansion.

“Trump’s wish to reclaim Panama, absorb Canada and purchase Greenland is preposterous on its face, but I think there’s an element of seriousness. It simultaneously serves to prepare the ground for the kind of dominant relationship that he would like to have over every other country,” Mr. Paris said. “But it’s not the 19th century any more.”

What is Trump trying to do?

A U.S. takeover of Canada to erase the former’s trade deficit started as an apparent joke by Mr. Trump at his Mar-a-Lago dinner with Mr. Trudeau in late November. He followed up with a string of mocking posts on his Truth Social network labelling Canada as the “51st state” and Mr. Trudeau as its “governor.”

Observers viewed the effort as a way to belittle the Prime Minister amid negotiations over border security and trade.

Mr. Trump is “hoping he can intimidate people and that’s why he’s trolling Trudeau on social media,” said John Bolton, who served as national-security adviser in the first Trump administration.

Over the past week, Mr. Trump has taken a more earnest tone in adding Greenland and Panama to the mix.

He accused Panama of perpetrating a “rip-off” of U.S. ships using the canal and demanded a reversion of the 1977 treaty in which his country agreed to give up ownership of the waterway. Then, he declared that “ownership and control of Greenland is an absolute necessity.”

Mr. Trump subsequently linked the three demands, with a meme showing him buying Canada, Greenland and the Panama Canal on Amazon. In a Christmas Day post, he erroneously asserted that “soldiers of China” run the canal, Canadians would pay 60 per cent lower taxes by joining his country and that Greenlanders “want the U.S. to be there.”

In addition to demanding a discount for shipping through the Panama Canal, Mr. Trump appears to be conflating the ownership of two canal-adjacent ports by a Hong Kong company with Beijing controlling the waterway.

Greenland, meanwhile, hosts a U.S. space force base in a strategic location between the U.S. and Europe, and has reserves of rare-earth minerals used in military technology.

What’s the history?

During his rise to the presidency in 2016, Mr. Trump assailed his own Republican Party’s disastrous invasion of Iraq more than a decade earlier. In this year’s campaign, he promised to end American military support to Ukraine.

Despite such isolationist policies, the president-elect has previously also evinced an expansionist bent. In his first term, he offered to buy Greenland from Denmark. When Danish Prime Minister Matte Frederiksen denied him, he called her “nasty” and cancelled a trip to Copenhagen.

Gerald Butts, Mr. Trudeau’s former principal secretary, has said that Mr. Trump also made the “51st State” comment to the Prime Minister during his previous administration.

Mr. Trump has outlined no plan to fulfill any of his annexation threats. He did not indicate, for instance, how he proposed to force Panama to turn over the canal.

And unlike the U.S.’s 1800s Louisiana and Alaska Purchases from France and Russia, respectively, it is virtually inconceivable any such arrangements would be made today. Ms. Frederiksen’s 2019 rebuff of Mr. Trump underlined that Greenland’s future was to be decided by Greenlanders, not by her government.

There is no indication that the island’s 57,000 residents, who since the 1970s have repeatedly elected governments supporting more independence and a Nordic model social safety net, have any interest in joining the U.S.

What has the response been?

The default Canadian response to Mr. Trump’s expansionism so far has been to dismiss it. Finance Minister Dominic LeBlanc referred to the 51st state line as “lighthearted” and “in no way a serious comment” earlier this month. Ottawa has also worked to appease Mr. Trump’s specific complaints over border security and trade.

Panamanian President José Raúl Mulino, by contrast, flatly rejected any negotiations with Mr. Trump, either about lowering shipping fees or turning over control of the canal. “The canal is Panamanian,” he told reporters. “There’s no possibility of opening any kind of conversation.”

Prime Minister Mute Egede of Greenland was similarly unequivocal. “We are not for sale and will never be for sale,” he said in a statement.

On Boxing Day, Mr. Trudeau tweeted a link to a 2010 report by NBC anchor Tom Brokaw extolling the virtues of the U.S.-Canada relationship. “Some information about Canada for Americans,” Mr. Trudeau wrote.

Some Canadians are pushing for a stronger response.

Mark Carney, the former central banker Mr. Trudeau has reportedly been trying and failing to woo to become finance minister, wrote on X that Mr. Trump was “carrying the ‘joke’ too far.”

“Time to call it out, stand up for Canada, and build a true North American partnership,” he wrote.

Vancouver Liberal MP Hedy Fry wrote Friday that Mr. Trump’s “trolling” might have been worth “an eye roll” the first time but “it is now tiresome.”

There is also the distinct possibility that Mr. Trump’s persistent jabs might backfire by hardening Canadian resolve.

“If Trump continues,” said Mr. Paris, now the director of the Graduate School of Public and International Affairs at the University of Ottawa, “he may stimulate Canadian nationalism in a way that no government program in Canada has ever succeeded in doing.”