Trump's obsession with Greenland may be ridiculous. But the idea behind it is serious.

This is an adapted excerpt from the Jan. 7 episode of "Alex Wagner Tonight."

On Thursday, former President Jimmy Carter’s six-day state funeral came to an end. The national service was attended by Carter’s family and friends, as well as President Joe Biden and all the living former presidents. This solemn occasion comes as Carter’s legacy has been thrust back into the news by incoming President Donald Trump.

“The Panama Canal is a disgrace, what took place at the Panama Canal. Jimmy Carter gave it to them for $1, and they were supposed to treat us well. I thought it was a terrible thing to do,” Trump said during a news conference on Tuesday. 

Trump’s fight with the recently deceased president has a lot to do with the president-elect’s newfound fixation on American territorial expansion, which, in turn, led to a bizarre declaration that the U.S. should regain control of the Panama Canal.

But to understand what’s going on in Trump’s mind here, you have to go all the way back to Jan. 9, 1964 — exactly 61 years ago this week.

At the time, anti-American riots had broken out in Panama, in part over U.S. control of the Panama Canal. That conflict sparked more than a decade of careful diplomacy spanning the administrations of four presidents, with the goal of handing control of the Panama Canal over to the people of Panama.

For most of that time, the negotiations in Washington were serious and bipartisan. With a few notable exceptions, Democrats and Republicans were largely aligned on the plan to negotiate a fair treaty to hand over control of the canal. A young moderate senator by the name of Joe Biden called the Panama Canal, “the last vestige of U.S. imperialism.” 

By 1976, the U.S. was in the final stages of negotiating a treaty with Panama’s leader, Gen. Omar Torrijos. But right around that time, some enterprising far-right conservatives realized that they could use the Panama Canal issue to gin up nationalist anger among the American public. They began arguing that America should leave the negotiations and keep control of the canal. 

The keep-the-Panama-Canal movement soon found a very charismatic messenger to push the cause: Ronald Reagan. The actor-turned-politician became the American avatar for the movement to try to keep the Panama Canal. At the time, Reagan was contesting Gerald Ford’s nomination as the Republican candidate for president in the 1976 election. Reagan made the Panama Canal a central issue of his campaign.

He ultimately lost that primary to Ford — and then Ford went on to lose the presidential race to Carter—but the Panama Canal issue did not go away, and neither did Reagan. The task of finalizing the agreement fell in Carter’s lap. 

Reagan laid the foundation for his next presidential run by challenging Carter at every step. He gave public speeches, he testified before Congress and he even held a public debate with fellow conservative William F. Buckley over the merits of keeping the canal.

But in 1977, Carter signed the treaty handing over control of the Panama Canal. “We are here to participate in the signing of treaties that will assure a peaceful and prosperous and secure future of an international waterway of great importance to us all,” Carter said at the time. “But the treaties do more than that. They mark the commitment of the United States to the belief that fairness and not force should lie at the heart of our dealings with the nations of the world.”

“Fairness, not force.” It was a powerful statement by Carter. But by that point, the issue had gone from a matter of diplomacy to a full-blown wedge issue, with protests outside the White House. And that movement was part of the coalition that helped propel Reagan to victory over Carter in 1980.

And yet, despite Reagan’s crusade, the treaty remained in place throughout Reagan’s presidency. Apparently, it wasn’t a major priority for Reagan once he was in office. But the germ of Reagan’s crusade against the Panama Canal Treaty idea lived on in the minds of other, populist-minded conservatives.

So as we prepare to re-enter the presidential administration of a man whose worldview remains stubbornly stuck in the 1970s and ‘80s, we are now re-litigating one of the most cynical debates in American foreign policy. And because this is Trump we’re dealing with, the foolish and ill-conceived imperial ambitions go far beyond just Panama.

During a news conference on Tuesday, Trump told reporters the United States needs Greenland for “national security purposes.” You may recall that Trump toyed with the idea of buying Greenland during his first presidential administration, even though the nation of Denmark says it has zero interest in handing it over to the U.S.

Trump also refused to rule out the idea of using military force to acquire both Greenland and the Panama Canal. Make of that what you will. 

The origins of Trump’s Greenland scheme are younger than Trump’s Panamanian fixation. As reporters Peter Baker and Susan Glasser reported in their book “The Divider,” Trump was first put on to the idea of acquiring Greenland by one of his billionaire friends, Ronald Lauder—one of the heirs to the Estee Lauder cosmetics fortune.

According to Glasser and Baker, Trump was so obsessed with the Greenland idea in his first administration that it “absorbed the National Security Council staff for months.”

Part of Trump’s fixation with Greenland may have stemmed from his failure to understand how maps work. No, really. Trump told Glasser and Baker, “I love maps. And I always said: ‘Look at the size of this. It’s massive. That should be part of the United States.’”

Now, if you look at a map of Greenland, it does appear to be massive. But that’s not because Greenland is actually massive. The earth is a sphere, and so when you lay it out on a flat map, all of the areas near the North and South Poles are stretched out to look bigger than they actually are. Greenland is still a pretty large territory but, in reality, it’s not nearly as big as it appears on a map.

Yet Trump appears to have become obsessed with the idea of acquiring Greenland, and maybe using the U.S. military to do so, because it looks “massive.” That is the level American foreign policy is about to be operating on.

On Tuesday, Trump also reiterated his desire to make Canada the 51st U.S. state, something Canadians also have precisely zero interest in. Trump also said he wants to rename the Gulf of Mexico the “Gulf of America,” because he thinks that sounds better.

All of this is obviously ridiculous — and in some ways a distraction from the things Trump might actually do as president — but the idea behind this territorial expansion is serious. As Reagan proved 50 years ago, the concept of America as an expansive global empire can be an intoxicating political force. 

While buying Greenland may be a fantasy, powerful nations like Russia and China are trying to expand their territorial control at all costs. America will have to decide if it wants to be on the side of sovereignty and self-determination or on the side of imperial expansion, however unhinged that expansion may be. A choice, as the late President Carter said, between fairness or force.

Allison Detzel contributed.