Today the most generous thing one could say about those statements is that they were wildly premature. Many foreign policy experts say he fundamentally misjudged the reactions of two major American adversaries. And neither seems to fear him — precisely the critique he leveled at Barack Obama back in the days when Mr. Trump declared America’s toughest national security challenges could be solved as soon as a president the world respected was in office.

The core problem may have been Mr. Trump’s conviction that economic incentives alone — choking off oil revenues in Tehran and the prospect of investment and glorious beach-front hotels in North Korea — would overcome all other national interests.

He dismissed the depth of Iran’s determination to re-establish itself as the most powerful force in the region, and Mr. Kim’s conviction that his nuclear arsenal is his only insurance policy to buoy one of the last family-controlled Stalinist regimes.

“After three years of no international crises,” Richard Haass, the president of the Council on Foreign Relations, wrote on Tuesday, Mr. Trump is “facing one with Iran because he has rejected diplomacy and another with North Korea because he has asked too much of diplomacy.”