The 81-year-old hunkered down at Camp David to regroup with wife Jill and family amid calls for him to withdraw from the upcoming election.
Biden was rambling and incoherent during last week’s TV clash with rival Donald Trump.
The First Lady, 73, is said to be the only one who could convince her husband to quit this year’s race for the White House.
But she told Democrat super-donors on Saturday that he was “the only person for the job.”
The President insisted at the rally in New Jersey that he had been able to win over more undecided voters than Trump.
He claimed research shows viewers were put off by the former President’s actions over the Capitol riots in January 2021.
And Biden said of his performance in the debate: “I didn’t have a great night, but I’m going to be fighting harder.”
Democratic National Committee chair Jaime Harrison shot down speculation of a plot to oust Biden before confirmation of the party’s candidate in August.
Political heavyweights including former President Barack Obama have publicly thrown their weight behind Biden.
But a campaign source said the President was “humiliated and devoid of confidence” following the debate disaster.
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