Watergate journalist Carl Bernstein said on CNN Monday night that sources have told him President Joe Biden has appeared similarly to how he did during last week’s debate more than a dozen times in the past 18 months, troubling those close to him.

“These are people, several of them who are very close to President Biden, who love him … and they are adamant that what we saw the other night, the Joe Biden we saw, is not a one-off,” Bernstein recounted to CNN’s Anderson Cooper. “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.”

Biden’s appearance in the debate against his competitor, presumptive GOP nominee Donald Trump, has prompted concern throughout the Democratic establishment. Calls to replace him as the 2024 presidential candidate have grown, and the president and his surrogates have been on damage control for days assuring voters his age — he is 81 — will not be an issue.

“Folks, I would not be running again if I did not believe with all of my heart and soul that I can do this job,” Biden told supporters in New York last week after the debate.

Regardless, a chorus of lawmakers have expressed reservations about the president and asked for more transparency. Sen. Sheldon Whitehouse (D-R.I.) said Monday he was “horrified” by Biden’s appearance and said he was among many voters who wanted to ensure his team “are being candid with us about his condition.”

Bernstein added in the interview Monday night that some of his sources have told him in the past six months there has been a “marked incidence of cognitive decline.”

“What these folks are saying and have been saying for a while is: ‘Yes, he’s great when we see him as we have tonight. But he also has these inexplicable moments that we are very concerned about,’” Bernstein said.

The journalist went on to say he’d been told Biden remained strong on foreign policy and retained the support of his staff. But Bernstein said questions have been growing that need answers.

“I have heard for two years how sharp Joe Biden is in his national security meetings,” he said. “He has an absolute command of the facts, he’s sharp as can be. … We’re clearly dealing with two sets of one person and it really needs to be explored according to the people I’m talking to.”

“But this is a problem that is not going to go away,” Bernstein added, “unless it’s explicable.”