The Mueller report revealed that Ms. Sanders had acknowledged that her repeated claim in 2017 that she had personally communicated with “countless” F.B.I. officials who told her they were happy with President Trump’s decision to fire James B. Comey as the agency’s director was a “slip of the tongue” and not founded on any facts.

Asked on “Good Morning America” if the report had damaged her credibility, Ms. Sanders responded that she had made the statement in the heat of the moment, and that it was not “a scripted talking point.”

But then she added, “I’m sorry that I wasn’t a robot like the Democrat Party that went out for two and a half years and repeated time and time again that there was definitely Russian collusion between the president and his campaign.”

It has been a hallmark of the Trump White House never to admit a mistake, never to apologize and never to cede a point. This case was no different.