Rep. Michael McCaul (R-Texas) is sounding the alarm about President Donald Trump's recurring hints at using military force to acquire Greenland. The former chair of the House Foreign Affairs Committee says any such move would be catastrophic for the NATO alliance—because it would effectively declare war on NATO itself.

A Military Move Would Flip NATO Inside Out

Speaking on ABC's This Week on Sunday, McCaul didn't mince words about what a Greenland invasion would mean. Greenland is a territory of Denmark, and Denmark is a NATO ally. That means Article 5—the mutual defense clause that treats an attack on one member as an attack on all—would come into play.

"For him to militarily invade would turn Article Five of NATO on its very head, and in essence, put us at war with NATO itself," McCaul explained. He went further: "It would end up abolishing NATO as we know it."

Here's the thing though: McCaul argues there's no reason to invade in the first place. The United States already has sweeping military access to Greenland under a defense agreement signed with Denmark back in 1951, right after World War II.

"The fact is, the president has full military access to Greenland to protect us from any threats," McCaul said. "If we want to put more military in there, we can. We don't have to invade it."

As for buying Greenland? McCaul says that's been floated by past presidents too. "If he wants to buy it, that's fine," he noted. "But I don't see a willing seller right now." Neither Denmark nor Greenland has shown any interest in entertaining offers.

Europe Rallies Around Denmark

European leaders aren't sitting quietly on the sidelines. European Commission President Ursula von der Leyen and French President Emmanuel Macron have both made clear statements defending Greenland's sovereignty and standing with Denmark.

Von der Leyen said she's been in contact with NATO and European heads of state, emphasizing that Europe will protect its strategic economic and security interests "with solidarity and resolve."

Macron doubled down on that message, stressing that France's actions are guided by national sovereignty and the UN Charter. France is even participating in Denmark's military exercise in Greenland focused on Arctic security. He condemned what he called intimidation and tariff threats, saying Europe will respond in a coordinated way.

Republicans and Europe Push Back on Trump's Tariffs

Trump has escalated his Greenland push by threatening tariffs against Denmark and other countries that oppose the idea. That's not sitting well with members of his own party.

Sen. Thom Tillis (R-N.C.) called the tariffs "bad" last week, warning they would help Russian President Vladimir Putin and Chinese President Xi Jinping. Sen. Lisa Murkowski (R-Alaska) went even further, calling them "punitive" and urging Congress to reclaim tariff authority from the executive branch.

Over in Europe, lawmakers are threatening to block approval of a major EU-U.S. trade deal in response to Trump's threats. The European People's Party said it can no longer support the agreement and wants plans to lower U.S. tariffs shelved. What started as talk about Greenland has quickly become a broader transatlantic trade fight.

The bottom line: What might have seemed like another Trump negotiating tactic is now creating real fractures in the Western alliance, with both European leaders and Republican lawmakers pushing back hard.