WASHINGTON — President Trump has no regrets. His staff has no defense.

After weeks of assailing reporters and critics in diligent defense of their boss, Mr. Trump’s team has been uncharacteristically muted this week when pressed about his explosive — and so far proof-free — Twitter posts on Saturday accusing President Barack Obama of tapping phones in Trump Tower during the 2016 campaign.

The accusation — and the F.B.I. director, James B. Comey, and the former national intelligence director, James R. Clapper Jr., emphatically deny that any such wiretap was requested or issued — constitutes one of the most consequential accusations made by one president against another in American history.

So for Mr. Trump’s allies inside the West Wing and beyond, the tweetstorm spawned the mother of all messaging migraines. Over the past few days, they have executed what amounts to a strategic political retreat — trying to publicly validate Mr. Trump’s suspicions without overtly endorsing a claim some of them believe might have been generated by Breitbart News and other far-right outlets.

“No, that’s above my pay grade,” said Sean Spicer, the White House press secretary and a feisty Trump loyalist, when asked on Tuesday at an on-camera briefing if he had seen any evidence to back up Mr. Trump’s accusation. The reporters kept at him, but Mr. Spicer pointedly and repeatedly refused to offer personal assurances that the president’s statements were true.