On the campaign trail, Donald Trump vowed to put an end to nation building abroad and mocked U.S. allies as free riders. “‘America first’ will be the major and overriding theme of my administration,” he declared in a foreign policy speech in April 2016, echoing the language of pre–World War II isolationists. “The countries we are defending must pay for the cost of this defense, and if not, the U.S. must be prepared to let these countries defend themselves,” he said—an apparent reference to his earlier suggestion that U.S. allies without nuclear weapons be allowed to acquire them.
Such statements, coupled with his mistrust of free trade and the treaties and institutions that facilitate it, prompted worries from across the political spectrum that under Trump, the United States would turn inward and abandon the leadership role it has played since the end of World War II. “