PALM BEACH, Fla. — Defending against criticism of his handling of the coronavirus, President Trump suggested the other day that he could hardly have been expected to be ready for such an unexpected crisis.

“Who would have thought?” he asked during a visit to the Centers for Disease Control and Prevention, the nerve center for the government’s response to the outbreak. “Who would have thought we would even be having the subject?”

Actually, quite a few people would have thought, and did — including the officials in his own White House who were in charge of preparing for just such a pandemic only to have their office shut down in a reorganization in 2018. “The threat of pandemic flu is the No. 1 health security concern,” one of the officials said the day before that happened two years ago. “Are we ready to respond? I fear the answer is no.”

For a president who lives in the moment, rarely planning too far ahead, the coronavirus has proved to be a leadership challenge he was not prepared for either. The outbreak that has rattled the nation does not respond to Mr. Trump’s favorite instruments of power: It cannot be cowed by Twitter posts, it cannot be shot down by drones, it cannot be overcome by party solidarity, it cannot be overpowered by campaign rally chants.