As President-elect Donald Trump prepares to assume later this month, he is ramping up his threats to take over a critical shipping artery and a strategic foreign land -- suggesting he could even use military force to do so.

"I'm not going to commit to that," Trump said on Tuesday when asked if he would rule out using the U.S. military to gain control of the Panama Canal and Greenland during a news conference at Mar-a-Lago.

"It might be that you'll have to do something. Look, the Panama Canal is vital to our country," he continued, also saying, "we need Greenland for national security purposes." He added, "We need them for economic security. The Panama Canal was built for our military."

Trump also slammed former President Jimmy Carter for overseeing diplomatic negotiations to turn over the Panama Canal, which the U.S. finished constructing in 1914 and controlled until Jimmy Carter ceded authority in 1977 with the Panama Canal Treaty.

"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.

Despite Trump's focus on expanding American territory, his strategy for achieving his objectives remains hazy -- and many of the claims the president-elect provided to rationalize the takeovers range from arguable to dubious, experts say.

They broadly agree that Greenland holds an important strategic location and is rich in lithium, graphite and other minerals. However, the world's largest island is already host to a U.S. military base and a longstanding treaty gives Washington significant control over Greenland's defense. Greenland and Denmark are also NATO allies.

"People really don't even know if Denmark has any legal right to it. But if they do, they should give it up because we need it for national security. That's for the free world. I'm talking about protecting the free world," Trump said.

On Panama, Trump has repeatedly claimed that the canal is "run by China," and that U.S. ships are charged more than vessels operated by other countries to cross through it.

"They don't treat us fairly. They charge more for our ships than they charge for ships of other countries. They charge more for our Navy than they charge for navies of other countries," he complained. "They laugh at us because they think we're stupid, but we're not stupid anymore."

In reality, the Panama Canal Authority (PCA) -- which is controlled by the Panamanian government -- operates the waterway, and 1977 diplomatic treaty with the U.S. mandates that all countries must be allowed to use it for "peaceful transit" and that there be "no discrimination against any nation, or its citizens or subjects, concerning the conditions or charges."

Accordingly, the tariffs and tolls associated with crossing the canal are determined by the size and type of the vessel and the cargo it carries -- not the flag the ship sails under. While the costs associated with using the waterway have risen in recent years, limits imposed on the canal's capacity due to a historic drought are behind the price hike.

China's expanding influence in Panama and across Central America more broadly has sparked concern on both sides of the aisle, but the same 1977 treaty authorizes the U.S. to intervene if the canal's neutrality is jeopardized.

Authorizing a military intervention with the intent of taking over the Panama Canal -- or Greenland -- is another matter.

Authorities of Panama and Greenland have repeatedly said they won't hand over any territory to Trump, with Panama's president declaring that the canal "is going to stay in our hands forever," and Denmark's prime minister insisting "Greenland is not for sale."

The U.S. Constitution gives Congress the sole ability to declare war on a foreign power, and -- once the war is declared -- gives the president wide-ranging authority to execute the conflict.

But presidents have often used military force without congressional approval, including against Panama.

In December 1989, former President George H.W. Bush launched an invasion of Panama to overthrow the country's de facto ruler, Gen. Manuel Noriega. The intervention, which was widely supported by the American public at the time, set Panama on a path toward democracy -- but was condemned by the United Nations as a violation of international law.

Trump has also said he could use economic pressure to force countries to capitulate to his agenda, including Canada, which the president-elect has repeatedly said should become the 51st state.

"Because Canada and the United States, that would really be something. You get rid of that artificially drawn line, and you take a look at what that looks like, and it would also be much better for national security," Trump said.

Canada's outgoing Prime Minister Justin Trudeau responded to Trump's statements in a post on X, writing "there isn't a snowball's chance in hell that Canada would become part of the United States."

"Workers and communities in both our countries benefit from being each other's biggest trading and security partner," he said.

Congress has delegated much of its foreign economic authority to the White House, but the biggest speed bump impeding Trump's ability to impose tariffs on Canada may be a trade deal negotiated under Trump himself: the United States-Mexico-Canada Agreement (USMCA).

The USMCA -- which is not due for review until 2026 -- allows any member to withdraw from it but requires that the exiting country wait six months before rescinding benefits to other parties.

The president-elect's clearest path to fulfilling one of his promises to redraw the world map may be renaming the Gulf of Mexico, which he vowed to change to "Gulf of America."

"What a beautiful name," he said. "And it's appropriate."