Former President Donald J. Trump went into sales-pitch mode immediately after Tuesday night’s debate, walking into the spin room to extol his own performance, crowing on Fox News and going on a late-night posting spree to hype unscientific online polls that he said showed he had crushed Vice President Kamala Harris.

“That was my best Debate, EVER, especially since it was THREE ON ONE!” Mr. Trump posted on Truth Social, minutes after the debate ended, referring to the two ABC News moderators.

Mr. Trump was insisting the same things privately to advisers and allies in the hours after the debate, according to three people with direct knowledge who spoke on the condition of anonymity to describe the private conversations. Mr. Trump appeared jubilant, as if he truly believed what he was telling them, the three people said.

But Mr. Trump’s actions after the debate told another story.

In the lead-up to his debate with President Biden in late June, Mr. Trump’s aides suggested that he might want to go into the spin room afterward. But he rejected the idea, and after his triumphant performance that night he felt no need to enter the spin room, understanding that his victory over the enfeebled president was so comprehensive that he could sit back and watch the press tear Mr. Biden apart.

His aggressive spinning on Tuesday night and Wednesday morning appeared to be an unspoken acknowledgment that his performance was suboptimal.

The day after Mr. Trump’s debate with Ms. Harris, his aides and his allies were largely echoing his praise of his performance in public, but privately several conceded that the former president had a rough outing, in stark contrast to his more controlled appearance against Mr. Biden.