Donald Trump was right. He inherited a mess. In January 2017, American foreign policy was, if not in crisis, in big trouble. Strong forces were putting stress on the old global political order: the rise of China to a power with more than half the productive capacity of the United States (and defense spending to match); the partial recovery of a resentful Russia under a skilled and thuggish autocrat; the discrediting of Western elites by the financial crash of 2008, followed by roiling populist waves, of which Trump himself was part; a turbulent Middle East; economic dislocations worldwide.

An American leadership that had partly discredited itself over the past generation compounded these problems. The Bush administration’s war against jihadist Islam had been undermined by reports of mistreatment and torture; its Afghan campaign had been inconclusive; its invasion of Iraq had been deeply compromised by what turned out to be a false premise and three years of initial mismanagement.

The Obama administration’s policy of retrenchment (described by a White House official as “leading from behind”) made matters worse. The United States was generally passive as a war that caused some half a million deaths raged in Syria. The ripples of the conflict reached far into Europe, as some 5 million Syrians fled the country. A red line about the use of chemical weapons turned pale pink and vanished, as Iran and Russia expanded their presence and influence in Syria ever more brazenly. A debilitating freeze in defense spending, meanwhile, left two-thirds of U.S. Army maneuver brigades unready to fight and Air Force pilots unready to fly in combat.