President Trump ought to pardon one of the earliest targets of the now-ended Mueller investigation, advised Sen. Rand Paul (R-KY).

Trump should pardon Michael Flynn, who served as Trump’s first national security adviser for a brief three weeks before being forced to resign because he misled Vice President Pence and the FBI over his communication with the Russian ambassador to the United States.

In the end, Flynn pled guilty to a single felony charge of making “false, fictitious and fraudulent” statements to the FBI and entered into a cooperation agreement with special counsel Robert Mueller as part of his investigation into any collusion between the Trump campaign and Russia. Flynn had also served as an adviser to Trump during his campaign.

The underlying case against Flynn is based on unconstitutional evidence, Paul argued.

“No American should be prosecuted for something they said in a private phone call unless a judge gave a warrant to the government and said they can listen to the phone call,” Paul said in an interview with Fox News. “They listened to General Flynn because they were spying on the ambassador. Okay, that’s foreign intelligence, but that shouldn’t be domestic prosecution. So what they did to Flynn––not only was it unfair, but I think should be unconstitutional. And I’ve been bugging the president for years to come forward and fix this for all Americans and say that no foreign intelligence gathering of information could ever be used against an American citizen in court for a crime unrelated to terrorism.

“So what they did to General Flynn was unfair, and I have told the president––he’s not responded to me––but I’ve told him my opinion is that he ought to pardon General Flynn,” Paul added.

Trump has used his presidential pardon power in several controversial cases, including former Arizona sheriff Joe Arpaio, but so far Trump has not used it with anyone connected to the Mueller probe.