Julián Castro slams Joe Biden and suggests his memory is failing: 'Are you forgetting what you said two minutes ago?'

In one of the most stunning moments of Thursday night's Democratic presidential primary debate, the former Secretary of Housing and Urban Development Julián Castro went after frontrunner and ex-Vice President Joe Biden on a subject most of his opponents have thus far avoided: his age.

The moment came while Castro was criticizing Biden's health care plan, saying it would leave vulnerable people like his grandmother to pay for insurance they couldn't afford. But Biden objected, saying his plan would be free for people who couldn't afford it and would only be a buy-in for people who could pay.

"They do not have to buy in," Biden said.

Castro fired back: "You just said two minutes ago that they would have to buy in! You said they would have to buy in! Are you forgetting what you said two minutes ago?"

While there have been some moments in the campaign thus far that have genuinely raised questions about Biden's mental acuity, this one did not. Castro seemed to be lashing out to cover for his own mischaracterization of Biden's plan and suggesting that an incomplete explanation of that plan would constitute a troubling memory lapse. It was a cheap shot.

Watch the clip below: