“I was frightened, because I had never ever seen Joe like that before or since. Never,” she said.
“As I watched it, I thought, ‘Oh, my God, he’s having a stroke.’ And it scared me to death.”
The former First Lady made the remarks in an interview that is set to air in full later this week.
But in the immediate aftermath of the debate, Mrs Biden was publicly supportive.
“You did such a great job, you answered every question,” she said at an event with her husband afterwards.
The oldest president in history at the time, Biden was already facing questions about his coherence and vitality.
The unprecedented withdrawal from a re-election campaign came after he had secured the nomination after a series of largely uncontested primaries.
“It was a mistake for the president to stay in the race as long as he did,” Democratic Senator Chris Murphy said today.
“We would’ve been better off as a party had he gotten out much sooner.”
Former Obama administration staffer Tommy Vietor thought likewise.
“I think this is how most voters felt while watching that debate, and why it was obvious that Biden had to drop out of the race,” he said.
“The impression left by Biden’s performance was unfixable, and pretending otherwise was insulting to voters.”
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