Trump’s Refusal to Rule Out Force Against a NATO Ally Sends Shockwaves Through Washington and Europe

WASHINGTON — President Donald Trump’s refusal this week to rule out the use of military force against a NATO ally has set off one of the most serious foreign-policy alarms of his presidency, deepening anxiety among U.S. allies and prompting rare bipartisan concern in Congress.

The moment came during an exchange with NBC News correspondent Vaughn Hillyard, who asked the president a question that, in previous administrations, would have elicited an immediate and unequivocal response.

“Do you commit to not militarily engaging NATO partners?” Hillyard asked.

“I don’t talk about that,” Mr. Trump replied.

Pressed again on whether he was unwilling to rule out attacking a NATO ally, the president declined to clarify.

The exchange, brief but stark, was quickly interpreted in Washington and European capitals as a significant escalation in Mr. Trump’s long-running rhetoric about Greenland, the autonomous Danish territory he has repeatedly suggested the United States should “acquire” for national security reasons.

A Line Presidents Traditionally Do Not Cross

For decades, American presidents of both parties have treated NATO’s core principle—Article 5, the collective defense clause—as inviolable. The United States has not merely pledged to defend its allies; it has relied on the assumption that alliance members would never contemplate military action against one another.

Mr. Trump’s refusal to take that option off the table has shattered that assumption.

“It’s not just provocative,” said one former senior U.S. diplomat, speaking on condition of anonymity. “It undermines the basic logic of NATO. If the United States won’t affirm that it won’t attack an ally, then the alliance ceases to function as a security guarantee.”

That concern is not theoretical. Denmark is a founding member of NATO. Greenland, while self-governing, is part of the Danish kingdom. Any use of force against Greenland would, under the alliance’s own framework, constitute an attack on a NATO member.

Congressional Alarm, Including From Republicans

The reaction on Capitol Hill was swift and unusually bipartisan. A group of lawmakers from both parties arrived in Denmark this week in what aides described as an emergency effort to de-escalate tensions and reassure allies.

Representative Don Bacon, a Nebraska Republican and former Air Force general, warned publicly that he would “lean toward impeachment” if the president were to order a military invasion of Greenland.

Such language is rare from a member of the president’s own party and underscores how far Mr. Trump’s comments have pushed the debate beyond conventional partisan lines.

Privately, several Republican lawmakers acknowledged that the president’s refusal to offer even a symbolic reassurance had left them scrambling to contain diplomatic fallout.

Implications for Global Power Politics

Former Justice Department official Andrew Weissmann argued that the signal sent abroad may be even more consequential than the domestic reaction.

“This tells Russia, this tells China, that the post-World War II system—the idea that borders aren’t changed by force among allies—is no longer a firm principle,” he said during a televised panel discussion.

Analysts noted parallels to Russian justifications for invading Ukraine, which relied on claims of historical entitlement and national security necessity. While the situations are not identical, the erosion of norms is what worries strategists.

“If the United States adopts a ‘might makes right’ posture toward its own allies,” one European security official said, “it becomes much harder to argue against that logic elsewhere.”

Greenland on Edge

In Greenland itself, the impact has been tangible. Danish and European military assets have increased their presence around the island in recent days, a move officials describe as precautionary but reassuring.

For many Greenlanders, the sight of military aircraft and naval vessels in a region prized for its isolation and calm has been unsettling.

“We are not for sale,” said a resident of Nuuk, Greenland’s capital, in an interview with reporters. “We are people who live here. We want to be respected.”

Greenland’s strategic value—its location in the Arctic, proximity to emerging shipping lanes, and vast untapped mineral resources—has long attracted global interest. But local leaders have emphasized that security concerns can be addressed through existing NATO frameworks, including expanded basing agreements, without violating sovereignty.

NATO Trust Under Strain

The controversy comes at a moment when trust in U.S. leadership is already strained. Mr. Trump has repeatedly criticized NATO members for defense spending levels, threatened punitive tariffs against allies, and questioned the value of long-standing security commitments.

European diplomats say the Greenland episode crystallizes a deeper fear: that American policy has become unpredictable to the point of strategic risk.

“NATO functions on credibility,” said a senior European official. “Not just military capability, but the belief that commitments mean something. Ambiguity on this question is destabilizing.”

Economic and Strategic Fallout

The implications extend beyond security. Several NATO countries are now openly discussing the need to reduce reliance on the United States not only for defense, but also for trade and investment.

Canada’s recent efforts to diversify trade relationships, including outreach to China and Gulf states, have been cited by analysts as part of a broader pattern. Allies are hedging against what they perceive as American unpredictability.

This diversification, experts warn, could have long-term consequences for U.S. influence, even if future administrations seek to repair alliances.

“Once countries build alternatives,” said a former NATO official, “they don’t simply dismantle them because Washington changes tone.”

Public Opinion and Political Risk

Polling consistently shows that a large majority of Americans oppose the use of force against allies and support NATO membership. That disconnect between public opinion and presidential rhetoric has heightened concern among lawmakers in both parties.

“This is not a popular idea,” said one Democratic senator. “It’s not even controversial. Americans overwhelmingly reject it. Which makes the refusal to rule it out all the more disturbing.”

A Precedent That May Not Fade

Perhaps the most lasting impact of the episode is the precedent it sets. Even without action, the refusal to reassure allies has already altered calculations abroad.

Future U.S. presidents may find that promises once taken at face value now require proof. Rebuilding trust, diplomats caution, is far harder than maintaining it.

For now, NATO leaders are watching closely, Greenlanders are preparing public demonstrations, and Congress is signaling that there are limits—even for a president—when it comes to threatening America’s own allies.

The immediate question is whether Mr. Trump will clarify his position. The larger one is whether the damage has already been done.