A former doctor for President Barack Obama claimed that Joe Biden, the Democrat frontrunner, “looked frail” when confronted by Sen. Kamala Harris (D-CA) over his record on civil rights at the first Democrat presidential debate last month.

Dr. David Scheiner, who served as Obama’s personal physician for more than 20 years prior to his election to the presidency, told the Washington Examiner on Friday that after having watched the debate, he was worried about the 76-year-old former vice president’s state of health.

The longtime Obama physician even drew comparison between Biden’s faculties and those of former Special Counsel Robert Mueller, who appeared weak, frail, and confused while testifying in front of the House Judiciary Committee this week.

“Harris started attacking him and he looked frail to me,” Scheiner said. “I sort of got the feeling he wasn’t very strong. It was similar to the feeling I got when Republicans started attacking Mueller so fiercely.”

Biden, who if elected would be the oldest president ever inaugurated, is generally perceived to have done poorly at the first debate. In particular, the former vice president struggled to defend himself in the face of a fiery rebuke from Harris over his recent praise for segregationists and long held opposition against busing to integrate public schools.

Instead of presenting an adequate rebuttal to Harris’s critiques, Biden attempted to dismiss her outright by claiming she had mischaracterized his record. He then proceeded to muddle his position on busing and inaccurately claim he never offered praise for racists, before conceding the argument by saying “my time’s up, I’m sorry.”

The poor performance renewed existing concerns about the former vice president’s capabilities as a candidate, and not just from opponents. After the debate, Biden’s team was reportedly “freaking out” about the way he handled the encounter with Harris. Federal Election Commission filings show his aides took the incident seriously enough to have hired a speech coach, best known for his work with President Bill Clinton, one day after the debate.