“Really hard,” Mr. Trump told journalists along for the ride.

White House officials, who had initially urged Mr. Trump to cut the tour into two separate trips to Asia, took pains to ease the load for the president. They built down time into his schedule almost every afternoon and made sure he had access, where possible, to familiar foods. Twice — as he was heading to Hanoi, and then from there to Manila — they diverted Air Force One on circuitous routes to allow Mr. Trump to depart earlier than planned from one stop and still stay on schedule for the next.

The president, though, did not take kindly to any hint that he might not be up to the journey. On Sunday, he chafed when North Korea’s state-run news agency responded to his Seoul speech by calling Mr. Trump a “lunatic old man.”

“Why would Kim Jong-un insult me by calling me ‘old’ when I would NEVER call him ‘short and fat?’ ” Mr. Trump shot back on Twitter, referring to the North Korean leader.

Even as Mr. Trump showed the first signs of fatigue at summit meetings during the final two days, he made sure other leaders took note of his staying power.

“We’ve had 12 days — I don’t know, how many days have you had there?” he said, turning to Prime Minister Narendra Modi of India at the start of their meeting on Monday.

He also made a point of noting that the press corps traveling with him was looking somewhat ragged.

“My press — I feel so sorry for them, they’re exhausted,” the president said as he departed midway through the summit meetings in Manila on Tuesday, skipping a group photograph and plenary session. “Would you like to stop in another couple of countries? Because we can do that if you want.”