Former New Jersey Gov. Chris Christie said Sunday that President Trump should be worried about prosecutors linking him to his former attorney Michael Cohen's criminal activities.

"You're not totally clear," Christie said on ABC's "This Week."

On Friday, Trump responded to a pair of sentencing memos from federal prosecutors following Cohen guilty pleas by writing on Twitter, "Totally clears the President. Thank you!"

Cohen pleaded guilty in August to financial crimes including a campaign finance violation for his work to pay women alleging affairs with Trump during the 2016 campaign. Trump argues there was no crime, and that silencing the women was not linked to his campaign.

Christie, a Republican who briefly led Trump's presidential transition team, said the sentencing memo filed against Cohen in New York features surprisingly strong language. Christie said that makes him suspect that federal prosecutors in New York may have corroborated Cohen's claim that he violated campaign finance law "in coordination with and at the direction of" Trump.

"The language sounds very definite. What I would be concerned about is what corroboration do they have," Christie said. "Everyone knows Michael Cohen is not going to be the most effective or trustworthy witness on the stand, given some of his past statements. The question is, they sounded very definitive. In my experience, the problem is, when prosecutors are that definitive, they have more usually than just one witness."

However, Christie added that "the flip side for the prosecutors is, they'd better have more than one witness. Because if you're shooting at the president of the United States and the only bullet in your gun is Michael Cohen, I think that is a problem."

A separate sentencing memo was filed Friday in Washington by special counsel Robert Mueller, after Cohen pleaded guilty to lying to Congress.

"I would say to everybody what I said to the president right from the beginning. There is no way you can make it shorter. but there's lots of ways you can to make it longer," Christie said. "And one of the ways to do that is to say you're in the clear when the prosecutor still has subpoena authority, the ability to indict people, and the ability to keep the investigation going. Until Bob Mueller shuts down, hands in the keys and his credentials back in, nobody's clear."