Trump says he’ll ‘acquire’ Greenland. Here’s what the Constitution says

President Donald Trump has made very clear his desire to “acquire” Greenland from Denmark, no matter the damage to NATO or to the US alliance with Europe.

What the White House has not done is spell out how Trump’s acquisition would take place. While Trump has not ruled out using the military, it would be an unprecedented use of the modern military to invade and claim for the US a semiautonomous territory despite domestic and international opposition. Two exceptions are the 1893 US-backed coup in Hawaii, something for which the US government apologized in 1993, and the bloody three-year Philippine-American War in 1899, when the US put down a rebellion by Filipinos after it took control of the Philippines from Spain.

The text of the Constitution and the example of history suggest that for a more peaceful option, Trump would need to ratify a treaty with Denmark and Greenland to buy the world’s largest island.

Ratifying a treaty, according to the Constitution, requires 67 senators, which in today’s political environment means Trump would have to convince Republicans and some Democrats to back him. He would also have to squeeze money for the purchase out of Congress. Meanwhile, some senators from both parties have introduced legislation to protect NATO by blocking Trump from acquiring Greenland.

Trump seems unlikely to let opposition in Congress get him down, so consider the 50-year odyssey required for the US to obtain what today are known as the US Virgin Islands … from, coincidentally, Denmark.

The US, led by then-Secretary of State William Seward, realized the strategic importance of the islands during the Civil War and tried to purchase the islands from a willing Denmark for $7.5 million. The two sides negotiated a treaty, which was approved by a vote in Denmark.

But the 1867 sale did not ultimately go through, according to a US State Department history, because the Senate failed to ratify the treaty. Without going too deep into the historical details, senators were angry at Seward over his support for the impeached President Andrew Johnson.

Today Trump has neither a purchase price nor the willing cooperation of Denmark or Greenland, much less a willing Senate.

In the early part of the 20th century, the US Senate did approve a treaty with Denmark to buy the islands, but this time the deal failed because the Danish parliament did not sign on.

It was not until World War 1 loomed that the US essentially threatened to occupy the islands. That threat was enough to make the sale happen, for $25 million in gold coin. The Senate approved the treaty in September of 1916 after the Danish parliament, its king, and a plebiscite (which is a fancy word for a direct election for all eligible voters) also approved. No vote was held for the islanders to weigh in, according to the State Department history.

The Constitution gives the president the power “by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur….”

Two-thirds of senators is a high bar — 67 if all senators are present and voting, which means Trump would need the support of some Democrats. But even some Republicans — among them Sen. Lisa Murkowski of Alaska, which the US bought from Russia for $7.2 million in 1867 — have expressed grave doubts about Trump’s Greenland plan.

The requirement of 67 senators to approve treaties may have something to do with the fact that presidents in recent decades have entered into agreements with foreign countries without offering them to the Senate for approval. These types of agreements are still binding under international law, but they have not been used to obtain territory.

The Constitution also gives Congress, not the president, the power to dispose of and manage federal lands and territories, although the executive branch conducts much of that business on a day to day basis.

When President Thomas Jefferson doubled the size of the US with the Louisiana Purchase (thanks, France), he worried he was exceeding his constitutional authority since the Constitution says nothing about acquiring lands. But he sent the agreement to the Senate anyway, and it was approved.