If former Vice President Joe Biden were President Donald Trump’s lawyer, he would advise him to “not sit down” with special counsel Robert Mueller because he doesn’t trust him to tell the truth, even if it’s unintentional.

“You’re in a situation where the President has some difficulty with precision,” Biden said during an interview with CNN’s Chris Cuomo Tuesday. “One of the things I would worry about if I were his lawyer is him saying something that was just simply not true without him even planning to be disingenuous.”

Biden’s comments follow news that President Donald Trump’s lawyers are discouraging him from sitting down with Mueller for an interview, as the special counsel probes Russian interference in the 2016 election. Trump has told reporters that he would be enthusiastic about meeting with Mueller, as he has consistently called the notion that his campaign colluded with Russia to win the election a “hoax” and a “witch hunt.”

Cuomo pressed Biden, asking if he thinks the President truly has “that little control” over the things he says.

“I just marvel at some of the things he says and does,” Biden said. “Like, what, two days ago, anybody that didn’t stand up and clap for him was ‘un-American?’And then maybe even ‘treasonous?’”

Cuomo pointed out that that remark was meant as a joke, according to the White House.

“Well, let me tell you, he’s a joke,” he said. “I think he understands, and I think the people around him understand, what Presidents say matter. Our children are listening, the world is listening. It matters what they say. And it’s just amazing the outrageously inaccurate things the President says.”

Biden’s stark criticism of Trump comes as the former Vice President publicly flirts with the idea of running for President in 2020. When asked about his potential bid on CNN Tuesday, Biden only vaguely shot it down, saying he would run only if his ambitions and the opportunity happened to line up.

Watch a segment of the interview below: