Senators McConnell and Tillis Break With Trump Over Potential NATO Withdrawal

When President Donald Trump told Reuters on April 1, 2026, that he was "absolutely" considering pulling the United States out of NATO — calling the 77-year-old alliance an ineffective "paper tiger" — it marked the sharpest confrontation between the White House and the transatlantic security order since the alliance's founding in 1949 [1]. Within 48 hours, two Republican senators broke publicly with their party's president, setting up a constitutional and political collision over the future of American commitments abroad.

The Break

Former Senate Majority Leader Mitch McConnell and Democratic Senator Chris Coons issued a joint statement on April 2, declaring: "The only time NATO has gone to war has been in response to an attack on America. NATO troops fought and died in Afghanistan and Iraq alongside American forces" [2]. McConnell, who chairs the Senate Appropriations Subcommittee on Defense, added that "Americans are safer when NATO is strong and united" and urged all allies to "tend this unity with care" [3].

Senator Thom Tillis of North Carolina went further. In a joint statement with Democratic Senator Jeanne Shaheen, Tillis called NATO "the strongest and most successful military alliance in history" and warned that American lives "would be lost in great numbers" without the alliance [4]. Tillis told ABC's "This Week" that it is "factually not true" that Trump can unilaterally withdraw from NATO, but conceded the president "can poison the well" and "make it functionally defunct if he wants to" [5].

The interventions carry different political weight. McConnell, 84, has championed NATO for nearly 40 years in the Senate and has clashed with Trump on foreign policy repeatedly, including on Ukraine aid. His interventionist worldview is longstanding and well-documented [6]. Tillis, by contrast, presents a more complicated case. He announced in early 2026 that he would not seek reelection after voting against Trump's "One Big Beautiful Bill" and facing threats of a primary challenge from the president himself [7]. With nothing left to lose electorally, Tillis's NATO dissent could be read as principled independence or consequence-free positioning — or both.

What Triggered the Crisis

The immediate catalyst was NATO allies' refusal to join the U.S.-Israeli military campaign against Iran, now in its second month [8]. A growing number of NATO partners resisted Washington's requests for support. Spain closed its airspace to U.S. military aircraft involved in the conflict. British Prime Minister Keir Starmer declared "This is not our war. We will not be drawn into the conflict," restricting U.S. bombers to defensive missions only from British bases [9].

Trump framed allied non-participation as evidence of NATO's irrelevance. In his April 1 address, he said the conflict's "core strategic objectives are nearing completion" while criticizing allies who had spent decades under America's security umbrella but refused to stand with it [10]. The war has resulted in the deaths of 13 U.S. service members, and a majority of Americans disapprove of the conflict according to recent polls [8].

The Legal Firewall

Whatever Trump's stated intentions, a significant legal barrier stands between rhetoric and withdrawal. The 2024 National Defense Authorization Act includes a provision stating that the president "shall not suspend, terminate, denounce, or withdraw the United States from the North Atlantic Treaty" without either two-thirds Senate approval or an act of Congress [11]. The provision was co-sponsored by then-Senator Marco Rubio — now Trump's Secretary of State — and Democratic Senator Tim Kaine [12].

The math makes formal withdrawal through Congress nearly impossible. Even if every Republican senator voted with Trump, at least 14 Democrats would need to join them to reach the two-thirds threshold. The 47-member Senate Democratic caucus would almost certainly oppose the move unanimously, and multiple Republican senators have signaled opposition [11].

But legal scholars caution that the statute's enforcement mechanisms are untested. Ilaria Di Gioia, writing in Time, notes that Trump "could seek to circumvent Congress' statutory constraint by invoking presidential authority over foreign policy" or frame withdrawal as a national defense necessity under Article II Commander-in-Chief powers [13]. The question of who has standing to challenge such a move in court remains unresolved. Congress itself would be the most plausible plaintiff, but with Republicans controlling the Senate, political appetite for suing a Republican president is limited [13].

Curtis Bradley of the University of Chicago notes that precedent exists — President Carter unilaterally withdrew from the U.S. mutual defense treaty with Taiwan in 1978 — but emphasizes that NATO withdrawal would be qualitatively different and "surprising" [13].

The Burden-Sharing Argument

Trump's frustration with allied spending levels predates the Iran crisis and predates his second term. Since his first presidential campaign in 2016, Trump has repeatedly demanded that NATO members meet the alliance's 2% of GDP defense spending guideline. The data shows that this pressure, combined with Russia's 2022 invasion of Ukraine, has produced measurable results.

Source: NATO / Atlantic Council

Data as of Jun 1, 2025CSV

In 2014, only three NATO members met the 2% threshold. By 2025, all 32 member states are estimated to meet or exceed it, with an alliance-wide average of 2.76% of GDP [14]. The frontline states of Eastern Europe lead the way: Poland spends an estimated 4.5% of GDP on defense, Lithuania 4.0%, Latvia 3.7%, and Estonia 3.4% [14].

Source: NATO

Data as of Jun 1, 2025CSV

At the June 2025 NATO summit in The Hague, allies endorsed an even more ambitious target: 5% of GDP by 2035, split between 3.5% on traditional defense and 1.5% on broader security-related spending. Meeting this target would require roughly $1.4 trillion in additional annual military spending across the alliance [15].

The steelman case for Trump's approach is straightforward: decades of quiet diplomatic pressure failed to move allied spending, while the combination of Russian aggression and Trump's confrontational tactics finally produced compliance. The White House itself has claimed credit, stating that "President Trump's leadership and vision" drove the NATO spending breakthrough [16]. Denmark and the United Kingdom announced increases to 2.5% and 3% of GDP respectively, while Latvia and Lithuania are targeting 5% [16].

Critics counter that the fixation on percentages obscures whether money is being spent effectively. The Center for Strategic and International Studies has argued that "NATO needs goals that focus on efforts to make effective use of its resources rather than seek random increases in spending" [17]. Spending 2% of GDP on pensions for retired military personnel, for instance, looks very different from spending 2% on deployable combat forces and modern equipment.

What a Reduced U.S. Role Would Mean

The United States maintains approximately 80,000 to 100,000 troops in Europe at any given time, a number that grew after Russia's 2022 invasion of Ukraine [18]. The Trump administration has already begun drawing down forces on NATO's eastern flank. In October 2025, the Pentagon withdrew the 2nd Infantry Brigade Combat Team of the 101st Airborne Division from Romania without replacing it, leaving roughly 1,000 U.S. troops in the country as the Pentagon shifted focus toward homeland defense and Latin America [19].

The capability gaps a full or substantial U.S. withdrawal would create are severe. According to analysis by Defense News and the International Institute for Strategic Studies, Europe depends on American assets in several areas where no substitute exists on a comparable timeline [20]:

Intelligence and surveillance: Europe has 49 military satellites compared to the U.S.'s 246. Analysts estimate 5–10 years to build sufficient independent capacity [20].

Suppression of enemy air defenses (SEAD): European NATO lacks the specialized aircraft and munitions to neutralize Russian integrated air defense systems. Most experts project a 10–15 year timeline to close this gap [20].

Long-range precision strike: Europe possesses some air-launched systems but lacks "arsenal depth and sea-based and land-based" alternatives, requiring 3–5 years for adequate capacity [20].

Nuclear deterrence: The July 2025 Northwood Declaration committed France and Britain to coordinate nuclear policy and operations — the most significant Anglo-French defense cooperation in decades. But questions remain about command authority, democratic mandate, and whether two small arsenals can substitute for extended American deterrence [21].

The IISS estimates that replacing U.S. capabilities would cost roughly $1 trillion over 25 years [21]. Several allied governments have stated or implied they cannot absorb these costs independently in the near term.

The Russian Threat Picture

The timing of the NATO debate coincides with assessments showing Russian military reconstitution proceeding faster than anticipated. Lithuania's 2026 national threat assessment reported that "brigades along the eastern borders of NATO countries are being expanded into divisions and completely new military units are being formed" [22]. A newly established missile brigade equipped with Iskander-M systems has been deployed to Russia's western military district, and upgraded radar systems in Kaliningrad now extend Russian airspace monitoring across thousands of miles [22].

Estonian intelligence has assessed that Russia's military-industrial complex has increased artillery ammunition production 17-fold since 2021, meaning Moscow can likely replenish reserves even while continuing operations in Ukraine [23]. Germany's Inspector General of the Bundeswehr, Carsten Breuer, has assessed that Russia will be "militarily ready to attack NATO countries by 2029 at the earliest" [24]. If a Russia-Ukraine peace deal occurs or Western sanctions are lifted, Lithuanian intelligence projects Russia could be prepared for limited military action in the Baltic region within one to two years [22].

The European Council on Foreign Relations and other analysts emphasize that the primary near-term risk is not a direct Russian attack on NATO but rather gray-zone operations — cyberattacks, sabotage, disinformation, and territorial provocations — designed to degrade European security while staying below the Article 5 threshold of collective defense [25].

Both sides of the NATO debate invoke the Russian threat to support their position. Proponents of continued U.S. commitment argue that this is precisely the wrong moment to signal wavering resolve. Trump allies counter that European dependence on American defense has become a structural problem, and that only the credible threat of withdrawal will force allies to develop self-sufficient capabilities before the Russian threat fully materializes.

The Political Arithmetic

The number of Republican senators willing to publicly oppose Trump on NATO remains small. McConnell and Tillis are the most prominent voices, but neither represents a large faction. McConnell has voted with Trump roughly 96% of the time during the current term, breaking primarily on Cabinet confirmations — voting against Pete Hegseth for Defense Secretary, Robert F. Kennedy Jr. for HHS, and Tulsi Gabbard for Director of National Intelligence [26]. Tillis voted with Trump approximately 98% of the time before his break over the "One Big Beautiful Bill" [26].

The Bipartisan Senate NATO Observer Group, co-chaired by Tillis and Shaheen, has issued statements defending the alliance, and the Air Force Times reported that a "bipartisan group of senators" has vowed to keep the U.S. in NATO [27]. But translating statements into binding legislation requires 60 votes to overcome a filibuster, and many Republican senators have remained silent rather than publicly challenging the president.

The 2024 NDAA provision already on the books may prove sufficient — not as an enforceable statute, but as a political signal that makes formal withdrawal procedurally prohibitive. The greater risk, as Tillis himself acknowledged, is that Trump does not need to formally withdraw to undermine the alliance. Reducing troop commitments, withholding intelligence sharing, publicly questioning Article 5, or simply creating enough uncertainty about American reliability can erode NATO's deterrent effect without triggering a single congressional vote.

What Comes Next

The McConnell-Tillis break is notable less for its immediate legislative impact than for what it reveals about the fractures within Republican foreign policy. McConnell represents the Cold War–era interventionist tradition that built NATO and sustained it through seven decades. Tillis, freed from electoral pressure, represents what he described as an "endangered species" of Republicans willing to embrace "bipartisanship, compromise, and independent thinking" [7].

Whether their dissent spreads to other Republican senators — particularly those facing competitive 2028 races in states with significant defense industry employment or military installations — will determine whether Trump's NATO threats remain rhetorical or acquire operational force.

NATO's one-year notice requirement for formal withdrawal means that even if Trump initiated the process today, the U.S. would remain a treaty member until April 2027 at the earliest [11]. The alliance has survived internal crises before — France withdrew from NATO's integrated military command in 1966 and did not rejoin until 2009. But no founding member has ever threatened full withdrawal, and no previous American president has done so while the alliance faces an active peer competitor rebuilding its military on Europe's eastern border.

The question is no longer whether American pressure can increase allied defense spending — the data shows it already has. The question is whether the president intends to use the alliance's acknowledged shortcomings as justification for an exit that would reshape the global security order, and whether Congress has both the legal tools and the political will to stop him.