In February 2024, when quizzed on President Joseph R. Biden Jr.’s ability to communicate his re-election message, Senator Chris Murphy, the Connecticut Democrat, quickly vouched for him.

“I know that he is ready for this campaign,” he told CBS News. “I have seen how effective he has been up close and personal.”

But five months into 2025, Mr. Murphy is on the leading edge of top Democrats aiming to Etch A Sketch away their past endorsements of Mr. Biden’s acuity. He told Politico this week that he had “no doubt” Mr. Biden suffered cognitive decline while in office.

Mr. Murphy, who declined to be interviewed for this article, is not alone in trying to reposition himself from a top Biden surrogate who sat on the campaign’s national advisory board to a truth-teller about what really happened in the 2024 campaign. His pivot is illustrative of a wide swath of the party that is hoping to atone for having fallen lock-step behind Mr. Biden.

Representative Ro Khanna of California, another Biden advisory board member who traveled the country as a surrogate to progressives, said this week that it was “obvious now” that Mr. Biden “was not in a condition to run for re-election.”

Mr. Khanna had vouched for Mr. Biden up until the president ended his campaign. A speech in Detroit that proved to be Mr. Biden’s last as a candidate “broke through” the political noise, Mr. Khanna said five days before Mr. Biden dropped out.