President Trump has already made news, and stoked controversy, by advocating unorthodox policies in unusual ways. In particular, he has signaled a foreign policy that breaks from decades of tradition — questioning alliances including NATO, arguing with allies such as Australia, and advocating an expansion of U.S. nuclear arms, among other things. Ultimately, many longtime foreign policy experts fear that he could undo an entire post-Cold War order and destabilize the international system.