White House hopeful Julián Castro defended his attack on Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE in the latest Democratic debate, insisting he was not targeting the former vice president's age during a feisty exchange on health care.

“I wasn’t taking a shot at his age, I was taking a shot at the fact that he had just said the words ‘buy in,’ you would have to ‘buy in,’ ” Castro, the former Housing and Urban Development secretary, said on ABC News in a post-debate interview.

The former Obama Cabinet member defended his tactics in the debate when he accused Biden of forgetting details of his health care plan and whether it would require a buy-in. Castro also claimed Biden was not carrying on Obama's legacy.

ADVERTISEMENT

The line of attack quickly provoked reactions among other Democratic presidential candidates, with Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.) saying that Castro's remark about Biden's memory was "not cool" and "so personal and so unnecessary.”

Meanwhile, Sen. Cory Booker Cory Anthony BookerThe movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-N.J.) seemed to back up Castro, saying the former San Antonio mayor had some "legitimate concerns" about Biden.

“I think there were a lot of moments where a number of us were looking on stage where he tends to go on sometimes,” Booker said on CNN after the debate. “There are definitely moments where you listen to Joe Biden and you just wonder.”

Asked directly if he was calling Biden, 76, too old for the presidency, Booker denied he was talking about the former vice president's age.

"I’ve listened to Joe Biden over the years, and often felt that there are times when he’s going on, or meandering in his speech," Booker said.

Both Biden and Castro's health care plans would provide a public option for people who are uninsured, though Biden had said during the debate that people "automatically can buy into this."

“But the difference between what I support and what you support, Vice President Biden, is that you require them to opt-in,” Castro said to Biden, noting that people would automatically be enrolled under his plan.

“Barack Obama Barack Hussein ObamaDemocrats ramp up pressure on Lieberman to drop out of Georgia Senate race The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE’s vision was not to leave 10 million people uncovered; he wanted every single person in this country covered. My plan would do that, your plan would not.”

“They do not have to buy in,” Biden responded.

“You just said that two minutes ago,” Castro shot back. “Are you forgetting already what you said just two minutes ago? I mean, I can’t believe that you said two minutes ago that they had to buy in, and now you’re saying they don’t have to buy — you’re forgetting that.”

While Republicans have previously attacked Biden over his age — and some have openly questioned his mental state — such discussions have rarely been as explicit among Democratic rivals themselves.

Castro defended himself late Thursday, saying he was focusing on the differences between the two plans and not on Biden’s age or state of mind.

“It’s not an attack on Vice President Biden, it’s not something about the personalities, it’s about the health care policy, that was the focus,” he told ABC.