Second-term presidents have another important trait: They tend to trust their instincts more. Getting elected once might mean you are lucky; getting elected twice must mean you are good. Mr. Trump has never been a shrinking violet when it comes to trusting his instincts. If he shocks the experts by holding the White House, he will be even more convinced that his methods and beliefs are right. Brimming with self-confidence and increasingly eager to make a mark in foreign affairs, Mr. Trump will return to his old agenda with new energy—and renewed contempt for the foreign-policy establishments here and abroad that despise him.

Mr. Trump’s second term would probably be driven by a quest for “deals,” transactional bargains with other leaders, even more so than in his first term. This could be disconcerting to those around him working to create the institutional basis for a long-term approach to the rise of China and security in the Indo-Pacific. For Mr. Trump, it is all leverage, and for the right deal he will make large and unconventional concessions. China, Russia, Iran, North Korea, Venezuela: Mr. Trump’s policy is likely to be a quest for dramatic if not always substantive or enduring deals…

A second term would be at least as chaotic as the first. This is not simply because the president is undisciplined and indifferent to process and bases his decisions on intuition more than analysis. For Mr. Trump, chaos is more than a choice or even a habit. It is a tool for keeping ultimate control in his own hands. That a presidential tweet can at any moment reverse a policy that aides have labored over for months infuriates, alienates and not infrequently humiliates his subordinates, but Mr. Trump stays in control. Keeping your associates and adversaries alike guessing is, in the president’s playbook, a tactic for success. Officials can always be replaced; power needs to be conserved.