But the first 16 months of Milley’s term, a period that ended when Joe Biden succeeded Donald Trump as president, were not normal, because Trump was exceptionally unfit to serve. “For more than 200 years, the assumption in this country was that we would have a stable person as president,” one of Milley’s mentors, the retired three-star general James Dubik, told me. That this assumption did not hold true during the Trump administration presented a “unique challenge” for Milley, Dubik said.