Throughout U.S. President Donald Trump’s most recent campaign and second term in office, he and his team have attempted to spin his foreign policy as pragmatic, disciplined, and strategic. They counter accusations that his global approach is impetuous and reckless with professions of “flexible realism”—a nod to an intellectual tradition often traced back to the Greek historian Thucydides, who famously observed that “the strong do what they can and the weak suffer what they must.” Although a diverse school of thought, realism generally holds that power is the currency of international politics. It eschews idealism and counsels a ruthless focus on defending national interest. The seeming resonance of this worldview with Trump's early-second-term foreign policy has led prominent analysts to embrace realism as the unifying framework for the president’s heterodox approach.…