WATCH: Former federal prosecutor explains why Trump will be 'indicted eventually'

Former federal prosector Andrew McCarthy, who also writes for National Review, predicted over the weekend that President Donald Trump will be "indicted eventually."

What did McCarthy say?

Speaking on "Fox and Friends" Sunday, McCarthy explained he doesn't believe Trump will be indicted as a result of special counsel Robert Mueller's investigation, which is investigating potential collusion and obstruction of justice. Instead, McCarthy said Trump is vulnerable to indictment by the Southern District of New York, the federal attorneys office that has targeted Michael Cohen, Trump's former personal attorney, for campaign finance violations.

"Will he be charged? Are they setting the stage to file charges against him? If you read that sentencing memo [that prosecutors wrote on Cohen], I can't come to any other collusion," McCarthy said.

However, McCarthy made it clear Trump will not be indicted while he is still president as per guidance from the Justice Department. Still, that doesn't mean Trump will not be indicted and charged if he loses re-election in 2020.

But if Trump wins re-election, he will likely not face criminal prosecution because the statute of limitations on campaign finance violations — which only span five years — "would have long run," McCarthy said.

In an op-ed for Fox News, McCarthy dove deeper into the details of Trump's legal conundrum, explaining at great length why he believes the president is vulnerable to criminal prosecution if he fails to win re-election.

At the heart of McCarthy's argument is that prosecutors with the Southern District of New York have laid the foundation for potential prosecution by inducing Cohen to admit, in court, that he made hush-money payments during the election "in coordination with and at the direction of" Trump.

"Prosecutors would not have done this if the president was not on their radar screen. Indeed, if the president was not implicated, I suspect they would not have prosecuted Cohen for campaign finance violations at all," McCarthy explained.