Anonymous sources said to be "very close" to President Joe Biden allegedly witnessed "15, 20 occasions" in which he showed signs of a mental decline during the last year and a half, legendary journalist Carl Bernstein told CNN Monday (July 1) night, days after Biden's disastrous performance in the first presidential debate last Thursday (June 27).

Bernstein, 80, who is credited for breaking the Watergate scandal alongside Bob Woodward, said the sources had previously seen "that horror show that we witnessed" while discussing Biden's debate performance with host Anderson Cooper.

“These are people, several of them who are very close to President Biden, who loved him, have supported him, and among them are some people who would raise a lot of money for him,” Bernstein said. “They are adamant that what we saw the other night, the Joe Biden we saw, is not a one-off, that there have been 15, 20 occasions in the last year and a half when the president has appeared somewhat as he did in that horror show that we witnessed.”

Bernstein said the situation is "significant" due to how "many people around the president are aware of such incidents, including some reporters incidentally who have witnessed some of them," though credited the president in other areas.

“But here we see tonight, as these people say, ‘President Biden at his absolute best,’" Bernstein added, referencing the president's criticism of the Supreme Court's immunity ruling in former President Donald Trump's legal cases Monday. “And yet these people who have supported him, loved him, campaigned for him, see him often say that in the last six months particularly, there has been a marked incidence of cognitive decline and physical infirmity.”

Biden, 81, the oldest president in history, appeared opposite Trump, 78, on the debate stage for the first time since the 2020 election and did little to quell concerns about his vigor and energy. The president appeared to struggle with his voice, clearing his throat and coughing multiple times, and was often seen open-mouthed and staring when Trump spoke, occasionally struggling to finish sentences.

Biden's performance reportedly led to "panic" among Democrats, according to longtime Democratic operative and CNN senior political commentator David Axelrod.

“He seemed a little disoriented. He did get stronger as the debate went on. But by that time, I think the panic had set in,” Axelrod said, adding that "there are going to be discussions about whether he should continue.”

Tawala Sharp