During the third Democratic primary debate, Julian Castro astonished fellow Democrats hinting front-runner Joe Biden is struggling with his memory.

Castro, 44, attacked Biden, 76, about his age following a question on health care.

‘Are you forgetting what you said two minutes ago?,’ Castro snapped at him during a fierce back-and-forth on healthcare as the audience gasped at the attack line.

‘Are you forgetting what you said two minutes ago?,’ he repeated as Biden looked shocked at the punches coming his way.

Biden was the main target of the night from the start when he got into a three-way tiff with liberal rivals Elizabeth Warren and Bernie Sanders on healthcare.

The former vice president attacked the cost of their proposed Medicare for All, sparking a 30 minute battle between the candidates on the health care issue.

Castro, who served as Secretary of Housing and Urban Development under President Obama, thanked the former president for his Obamacare plan and then pivoted to attack Biden for his healthcare plan, which is extension of Obamacare.

‘We owe a debt of gratitude to President Barack Obama. Of course, I also worked for President Obama, Vice President Biden, and I know that the problem with your plan is that it leaves 10 million people uncovered,’ he said.

‘Now, on the last debate stage in Detroit, you said that wasn’t true when Senator Harris brought that up. There was a fact check of that, they said that was true,’ Castro added.

He then when on to layout his healthcare plan and get in another shot at Biden, the frontrunner for the Democratic nomination.

‘I want every single American family to have a strong medicare plan available. If they choose to hold onto strong, solid private health insurance, I believe they should be able to do. But the differences between what I support and what you support, Vice President Biden, is that you require them to opt in and I would not require them to opt in, they would automatically be enrolled. That’s a big difference, because Barack Obama’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,’ he said.

Biden defended his plan: ‘They do not have to buy in. They do not have to buy in.’

And then Castro attacked him hard, implying he had forgotten what his plan involved in a not-so-subtle hint at the concerns among some Democrats about Biden’s age.

‘You just said that two minutes ago. You just two minutes ago they would have to buy in,’ he said.

‘Are you forgetting what you said two minutes ago? Are you forgetting already what you said just two minutes ago? 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 in. You’re forgetting that,’ Castro added.

‘You are automatically enrolled, ‘ Biden responded.

But Castro stayed on the attack.

‘If you lose your job, for instance, his health care plan would not automatically enroll you. You would have to opt in. My health care plan would. That ice a big difference. I’m fulfilling the legacy of Barack Obama and you’re not,’ Castro said.

‘That will be a surprise to him,’ Biden snapped back.

Earlier in the debate, when talking about his plan in comparison to Medicare for All, Biden said: ‘If you want medicare, if you lose the job from your insurance company, from your employer, you automatically can buy into this. You don’t have no pre-existing condition can stop you from buying in. You get covered. Period.’

Biden has faced questions about his mental ability to take on President Donald Trump after a series of verbal gaffes but questions about his health rose after his eye was seen filling with blood during a CNN town hall debate on the climate on Wednesday night.

If elected, Biden would be the oldest person ever to occupy the Oval Office.

He has said he will release his medical records and questions about his health are fair but his campaign has not said when those records will be made public.

After the fight between Castro and Biden, Pete Buttigieg stepped in to call for an end to the bickering.

‘This is why presidential debates are becoming unwatchable. This reminds everybody of what they cannot stand about Washington. Scores points against each other. Poking at each other. And telling each other that – my plan, your plan,’ he said.

But Castro interrupted to attack him too.

‘That’s called the Democratic primary election, Pete,’ Castro said. ‘That’s called an election. That’s an election. You know? This is what we’re here for. It’s an election.’