One of the standout moments from last night's Democratic debate came when candidate Julián Castro clashed with Joe Biden over health care.
"Are you forgetting already what you said two minutes ago?" Mr Castro said, before adding: "I’m fulfilling the legacy of Barack Obama and you’re not."
As the clear frontrunner, Joe Biden was always going to come under attack from his rivals.
Last night, he faced criticism over his support for the Iraq war and the deportation of migrants under the Obama administration.
But Joe Biden also went on the attack, criticising the health care policies of his two main rivals Bernie Sanders and Elizabeth Warren.
He said their plans were too expensive and he accused them of failing to explain how they would pay for the reforms.
Joe Biden is not the best debater. He frequently stumbles over his words, makes mistakes and gives long, rambling answers.
At one point last night he was asked about slavery and ended up talking about children listening to record players at night to learn words.
He’s also had gaffes on the campaign trail, misspeaking while addressing supporters and mixing up stories.
Despite all his flaws however, he remains extremely popular among Democrats and, if the opinion polls are to be believed, is likely to be the party’s nominee.
Julián Castro’s questioning of Joe Biden’s memory won’t go down well with supporters and could end up being a comment Mr Castro hopes voters will forget.
