The argument over Greenland has threatened to reignite a trade war with Europe and upend the NATO alliance that underpins Western security.

The time for flattering Donald Trump is over and Europe should hit back hard economically if the U.S. imposes tariffs on NATO allies that sent troops to Greenland, ex-NATO boss and former Danish Prime Minister Anders Fogh Rasmussen said on Tuesday.

Trump embarked on an overnight social media spree early Tuesday, sharing private messages from French President Emmanuel Macron, posting a fake image of U.S. control over the Arctic territory and claiming that there was “no going back” on his desire to seize the semi-autonomous island, which falls under the boundaries of Denmark, a NATO ally.

TIME spoke to legal experts about whether Trump could legally pull the U.S. out of NATO and the wider implications.

President Donald Trump reiterated his desire for the United States to control Greenland in a series of overnight Truth Social posts.

The president shared a private message from France's Emmanuel Macron, part of a flurry of activity as he added new fuel to his clash with Europe over the Arctic territory.

Russia’s Foreign Minister said Trump’s actions upended the Western concept of the “rule-based global order” that Russia has long criticized.

Denmark, Norway, Sweden, France, Germany, the United Kingdom, the Netherlands and Finland are casting a united front after Trump threatens tariffs.

Sen. Mark Warner (D-VA) told Special Report on Monday that President Donald Trump's "obsession" with securing a Nobel Peace Prize is shaping his foreign policy decisions and putting NATO at risk. BRET BAIER,