U.S. President Donald Trump on Wednesday cast fresh doubt on NATO’s reliability, saying he was not convinced the alliance would come to Washington’s aid in a crisis, as tensions rose over the White House’s renewed push to acquire Greenland.

“I DOUBT NATO WOULD BE THERE FOR US IF WE REALLY NEEDED THEM,” Trump blasted on Truth Social, while insisting the U.S. would still defend alliance members. “We will always be there for NATO, even if they won’t be there for us.”

Under Article 5 of the North Atlantic Treaty, NATO’s collective defense clause, an attack on one member of the alliance is considered an attack on all. The provision has been formally invoked only once — in response to al-Qaida’s 9/11 terror attack against the U.S.

Trump’s remarks came a day after the White House said it was not ruling out military action to acquire Greenland from Denmark, a NATO ally. Trump has repeatedly criticized the alliance and has long pressured members to boost defense spending, calling for increases from 2 percent of GDP to as much as 5 percent.

His new comments follow days of escalating rhetoric over Greenland, a self-ruling Danish territory. The White House said late Tuesday that Trump was “discussing a range of options” to acquire the massive, mineral-rich Arctic island, stressing that the use of U.S. military force was not off the table.

In his post, Trump said that military allies were failing to pay their fair share before his first term, while relying on the American security umbrella, and argued that without the U.S., Russia and China would “have zero fear of NATO.”

Danish Prime Minister Mette Frederiksen warned Monday that an American attack on another NATO country would mean “everything stops, including NATO and thus the security that has been established since the end of the Second World War.”

European leaders moved quickly to push back.

On Tuesday, eight of Europe’s top leaders said Greenland’s security must be ensured collectively through NATO and with full respect for sovereignty and borders.

On Wednesday, French Foreign Minister Jean-Noël Barrot said Paris was working with European partners on a joint response, while officials in Berlin confirmed discussions were underway on safeguarding Greenland’s sovereignty.

In his post, using an incorrect spelling for the iconic global award, Trump added: “Without my involvement, Russia would have ALL OF UKRAINE right now. Remember, also, I single-handedly ENDED 8 WARS, and Norway, a NATO Member, foolishly chose not to give me the Noble Peace Prize. But that doesn’t matter!”