President Donald Trump reportedly wants to buy Greenland, the world’s biggest island. Denmark, unsure whether the former property developer is joking, isn’t selling.

A Wall Street Journal report outlining the U.S. president’s apparent interest in striking a deal has left Danes bewildered, with a former prime minister asking whether it was a joke. Another prominent opposition member said the report indicates that Trump is “insane,” while a member of the government bloc called it a “terrible idea.”

But according to the Wall Street Journal, which cites people familiar with the deliberations, Trump has repeatedly expressed interest in striking a deal to purchase the island, and even asked his White House counsel to explore the idea.

Trump’s suggestion “must be an April Fool’s Day joke,” albeit out of season, tweeted Lars Lokke Rasmussen, who was prime minister until June and now heads the opposition in Denmark. Meanwhile, in the U.S., the idea is being taken seriously in some corners. Republican Rep. Mike Gallagher, R-Wis., tweeted that the suggestion isn’t “crazy,” adding that the U.S. “has a compelling strategic interest in Greenland, and this should absolutely be on the table.” Democrats appeared less enthusiastic, with Rep. Steve Cohen, D-Tenn., tweeting that the idea was one for the “cryonic memorial.”

The Wall Street Journal report comes as Trump prepares to make his first formal visit to Denmark, where he will meet with Prime Minister Mette Frederiksen and attend a state dinner hosted by Queen Margrethe II on Sept. 2-3. The meeting will focus, among other things, on Greenland, where the U.S. has built several military bases and weather stations since WWII. In 1968, a B-52 bomber carrying nuclear weapons crashed near the Thule air base in northwestern Greenland, causing radioactive contamination.

Frederiksen, who became prime minister after her Social Democratic party won elections in June, will make her first official visit to Greenland next week during which she’ll conduct formal talks with the island’s premier, Kim Kielsen. Greenland has home rule, but defense and foreign affairs remain under Danish governance. The island has representation in Washington D.C. and in the European Union.

More than 80% of Greenland’s 2.2 million square kilometers (830,000 square miles) are covered in ice, and the island has attracted considerable attention recently amid concerns that climate change is causing that ice to melt at a record pace. Greenland’s population of just 56,000 is concentrated around its coast lines.

The Wall Street Journal noted that it’s unclear how Trump would go about acquiring the Danish territory and said that neither the White House nor the State Department responded to a request for comment.

Worth Knowing About Greenland:

• Greenland, which sits in the North Atlantic Ocean between Europe and America, is at the nexus of geopolitical tensions that have long existed between the U.S., Russia, Canada, Denmark and Norway, which have all sought ownership of the natural resources in the North Pole.

• In 2014, Denmark staked a claim to roughly 900,000 square kilometers of the continental shelf in the Arctic Ocean based on its geological link to Greenland, according to a survey conducted by Danish authorities.

• More recently, China has joined the land rush by bidding on two airport construction jobs in Greenland. But last year, Denmark opted for joint funding with Greenland to prevent China getting control.

• Greenland, which gets most of its income from fishing and related industries, had a gross domestic product of just over $2.7 billion in 2017, according to its statistics office. The island receives an annual subsidy of about $500 million from Denmark.