When President Donald Trump entered office under an “America First” banner, it seemed to herald a new era of U.S. isolationism. As he prepares to leave the White House on Jan. 20, though, the shifts in America’s military engagements during his one-term presidency have been less dramatic than anticipated. Though their numbers are down, U.S. troops are still stationed in Afghanistan—for now. And instead of operating around a clear security strategy, Trump’s tenure was marked by its unpredictability—dramatic reversals, erratic interventions and the fraying of long-standing alliances.
Trump’s isolationist instincts came into regular tension with his closest advisers, many of whom espoused a more traditional view of American power projection. This was never clearer than in December 2018, when Trump ignored his aides and announced his decision to pull all U.S. troops out of Syria, prompting then-Defense Secretary Jim Mattis and other high-ranking officials to resign in protest. Trump subsequently softened his rhetoric, without definitively articulating a final policy, contributing to the sense of uncertainty over America’s security policymaking. The entire process was repeated in October 2019, only this time the decision triggered not resignations, but outrage among even Trump’s closest Republican supporters in Congress.
Meanwhile, Trump’s vision didn’t stop his advisers from hinting at military intervention as a path to regime change in places like Venezuela and Iran. In the latter case, Trump subsequently made his opposition to war clear. His broader reluctance to commit U.S. forces to another major conflict in the Middle East played a part in the deescalation of tensions with Tehran in January, following the U.S. killing of a top Iranian military commander, Maj. Gen. Qassem Soleimani, and Iran’s retaliatory ballistic missile strike against U.S. forces stationed in Iraq.
Over the course of his four years in office, Trump’s America First agenda has actually taken its heaviest toll on long-standing alliances. While he has taken credit for moderate increases in European defense spending, it has come at a cost. His vocal criticisms of NATO have weakened the alliance’s cohesion, and his demands for increased burden-sharing by South Korea and Japan for U.S. forces based in those countries have also strained relations with both Seoul and Tokyo.
There have also been some significant and perhaps durable shifts. The administration positioned economic security as central to national security and justified its increasing use of tariffs on those grounds. Immigration, particularly along the border with Mexico, became a key focus of the security agenda. And Washington has pulled back from counterinsurgency efforts, even as the Islamic State regroups as a terrorist movement. While President-elect Joe Biden is certain to adopt a dramatically different approach on these issues, he will find it harder to ignore them.