If Trump Pulls Out, the Alliance Would Likely Fall Apart
Last month, NATO, the world’s most successful military alliance, celebrated its 75th anniversary. Some fear that it may have been its last anniversary with the United States playing a leading role. Former U.S. President Donald Trump still views the alliance as obsolete. If reelected, he says he would encourage Russian leaders to do “whatever the hell they want” to member states that do not pay what he considers to be enough for defense. A second Trump presidency could have dire implications for European security.
Trump’s defenders argue that he is bluffing to pressure Europe into spending more on defense. But former U.S. officials who worked closely with Trump on NATO during his tenure, including one of us (Hooker), are convinced he will withdraw from the alliance if he is reelected. Trump hugely resents the more moderate advisers who kept him in check during his first term. If he reaches the White House in 2025, the guardrails will be off.
The U.S. Congress is concerned, too. It recently enacted legislation to prohibit a president from withdrawing from NATO unless Congress approves, either by a two-thirds vote in the Senate or an act of both houses of Congress. But Trump could circumvent this prohibition. He has already raised doubts about his willingness to honor NATO’s Article 5 mutual defense clause. By withholding funding, recalling U.S. troops and commanders from Europe, and blocking important decisions in the North Atlantic Council (NATO’s top deliberative body), Trump could dramatically weaken the alliance without formally leaving it. Even if he does not withdraw American support completely, Trump’s current position on NATO and his disinterest in supporting Ukraine, if adopted as national policy, would shatter European confidence in American leadership and military resolve.
EUROPE, ABANDONED
If Trump is reelected and follows through on his anti-NATO instincts, the first casualty would be Ukraine. Trump has opposed additional military aid to Kyiv and continues to fawn over Russian President Vladimir Putin. NATO Secretary-General Jens Stoltenberg is already trying to Trump-proof aid to Ukraine by coordinating it under the aegis of the alliance rather than the U.S.-led Ukraine Defense Contact Group. Should the United States weaken or terminate its defense commitment to Europe under Trump, European countries would feel more vulnerable and may become increasingly reluctant to send Ukraine their own vital military supplies. With dramatic aid cuts, Kyiv could be forced to negotiate an unfavorable agreement with Moscow that would leave Ukraine a rump state militarily and economically vulnerable to Russia. Should Ukraine’s defenses collapse altogether, brutal repression and forced Russification await some 38 million people.
The disastrous consequences would only start there. A deflated NATO would struggle to mount an effective conventional deterrent against further Russian aggression. Russia is now on a war footing, spending six percent of its GDP on defense, and its authoritarian leader is committed to an ultranationalistic mission to consolidate his rule over what he calls the “Russian world,” an unspecified geographic space that extends well beyond his country’s internationally recognized borders. Moscow could reconstitute its armed forces relatively quickly. After subjugating all of Ukraine, Putin would probably focus on the Baltic states—NATO members covered by the alliance’s security umbrella but claimed as historic Russian lands by Putin. Should NATO’s conventional deterrence be weakened by the withdrawal of U.S. support, Russia would only be tempted to act more brazenly.
NATO countries collectively now spend two percent of GDP on defense, but in the absence U.S. support, European armies are still not sufficiently prepared, equipped, and able to fight against a major-power adversary. Europe remains heavily reliant on the United States in several important areas. On its own, it lacks many of the key tools necessary for successful defense, including airlift capabilities, air-to-air refueling, high-altitude air defense, space assets, and operational intelligence—these are all supplied primarily by the United States. Without American help, NATO would lose much of its military edge over Russia. Europe’s defense industry remains badly fragmented, and developing the needed defense capacities to compensate for the loss of American backing could take the remainder of this decade.
A deflated NATO would struggle to mount an effective conventional deterrent against further Russian aggression.
Should the United States abandon NATO, the erosion of nuclear deterrence would severely compound Europe’s conventional deterrence problem. Nuclear weapons underpin the United States’ commitment to defend its allies and its nuclear capabilities form the bedrock of NATO’s capacity for deterrence. Should Trump close the American nuclear umbrella, Europe would have to rely on less than 600 British and French strategic nuclear warheads, a fraction of Russia’s total force of over 5,000 strategic and tactical nuclear warheads. Since Europe has no tactical nuclear weapons, it can hope to deter a Russian tactical nuclear attack only by threatening escalation to the strategic level, a move that Moscow may not find credible. In an attempt to scare Europeans away from backing Ukraine, Russia has on many occasions hinted it might use tactical nuclear weapons. Unlike the United States, France and the United Kingdom have not extended their nuclear deterrent to protect their allies. Should Washington leave Europe to fend for itself, Moscow might calculate that it could successfully resort to nuclear blackmail to capture the territory of NATO member states.
Without U.S. leadership in NATO, cohesion and unity among members would be difficult to maintain. It often requires a strong American voice to bring disparate member states to a consensus. Since NATO’s founding, a U.S. general officer has led the organization’s command structure, overseeing the military activities of all NATO member states. It is doubtful that any other country in the alliance could play this role.
NATO without the United States might limp along, but it is more likely that the alliance would collapse altogether. The European Union is not in a position to take NATO’s place any time soon, as its military capabilities are limited and more capable of managing regional crises than fighting major wars. Even if a rump NATO survives without strong American involvement, the challenges of divided leadership, inadequate deterrence capabilities, and an assertive adversary would heighten the risk of war with Russia, a major power bent on overturning the liberal international order.
THE FALLOUT
The damage would not be limited to Europe. If Trump wants to withdraw from NATO to punish allies for their inadequate defense spending, why would the United States maintain its commitments to its Asian allies, many of whom currently spend even less than NATO countries? For now, the defense ties between the United States and its allies in Asia, such as Australia, Japan, and South Korea, are growing stronger in the face of Chinese provocations. But a lack of confidence in U.S. commitments may well lead some of these countries to pursue nuclear weapons to offset China’s and North Korea’s nuclear advantages, undercutting the fragile stability that has prevailed in the region for decades. The withering of U.S. global leadership would also have profoundly negative consequences in the Middle East, where U.S. forces and U.S.-led coalitions are needed to deal with terrorist threats.
The United States’ economy might also suffer. Should a breakdown of deterrence trigger a general war with Russia or China, the economic costs would be staggering. Just a few Houthi fighters in Yemen have been able to disrupt global shipping through their attacks in the Red Sea. Imagine the consequences of a war among major powers. Moreover, trade ties often follow security ties. Last year, two-way transatlantic trade in goods topped $1.2 trillion. The United States has about $4 trillion invested in European industry. Some five million Americans work in European-owned industries. The United States has a huge economic stake in maintaining a peaceful Europe.
The United States has been here before. Before both world wars, Washington sought neutrality. Neither effort at isolationism worked and only prevented the United States from being able to help deter the aggressors in those wars. Eventually, the United States was pulled into both conflicts. After World War II, having learned the dangers of isolationism, the United States remained engaged and paved the way for the founding of NATO and 75 years of relative peace in Europe. The United States must not forget the painful lessons of the last century. To do so would risk undercutting U.S. global leadership, undermining the Washington-built international order, and making the world safer for authoritarian rule.