Key keywords: Donald Trump, NATO withdrawal, US foreign policy, 2024 US presidential election, transatlantic alliance, NATO collective defense, European security, NATO 2% defense spending target For months, former U.S. president and 2024 Republican presidential nominee Donald Trump has repeated a familiar threat at campaign rallies and media interviews: if he wins a second term in the White House, he will pull the United States out of the North Atlantic Treaty Organization (NATO), the 75-year-old transatlantic security alliance that has been the backbone of Western defense since the end of World War II. But a growing number of foreign policy analysts and European policymakers argue that Trump has already done irreversible damage to the alliance, even without formal withdrawal paperwork. During his first term from 2017 to 2021, Trump repeatedly questioned the value of NATO, called the alliance “obsolete” in early campaign remarks, and threatened to withhold U.S. defense support for member states that failed to meet the NATO-agreed target of spending 2% of their GDP on national defense. At the 2018 NATO summit in Brussels, multiple senior administration officials later confirmed that Trump came within minutes of announcing a U.S. withdrawal from the alliance, only backing down after last-minute appeals from his national security team and European leaders. Since leaving office, Trump has escalated his anti-NATO rhetoric. In a February 2024 campaign rally in South Carolina, he told supporters that he would encourage Russia to “do whatever the hell they want” to NATO members that fell short of the 2% spending target, a comment that drew widespread condemnation from both Democrats and mainstream Republicans in Congress, as well as panicked reactions from European capitals. The core of NATO’s strength lies in Article 5 of its founding treaty, which states that an armed attack against one member is considered an attack against all, requiring all signatories to come to the defense of the attacked state. This provision relies entirely on mutual trust: allies have to believe that other members, particularly the U.S. which contributes the largest share of NATO’s military capabilities, will follow through on their pledge even when it is costly. Trump’s repeated threats have already shattered that trust for many European governments. Over the past three years, EU member states have increased defense spending by more than 20% collectively, and launched multiple joint defense projects aimed at building a self-sufficient European security architecture that does not rely on U.S. support. Multiple senior European officials, including EU foreign policy chief Josep Borrell, have publicly stated that Europe can no longer count on the U.S. security guarantee, and must take its defense into its own hands. In this sense, Trump’s goal of weakening or dismantling NATO is already partially realized. Even if he loses the 2024 election, the shift in European defense policy and the erosion of transatlantic trust will take decades to reverse. If he wins, a formal withdrawal is likely the final step of a process he already set in motion years ago.