A former federal prosecutor explained why it would be "stupid" for President Donald Trump to pardon his longtime lawyer Michael Cohen.

Cohen split with the president in an interview with ABC News, breaking his silence on the criminal investigation he's at the center of.

The interview fueled speculation that Cohen is preparing to "flip" and cooperate with prosecutors.

A former federal prosecutor explained to Business Insider that it would be counter-productive for President Donald Trump to pardon his longtime lawyer Michael Cohen following the ABC News interview in which he broke his silence on the federal criminal investigation he's at the center of.

"Some people are speculating that this is Michael Cohen making a final threat/plea to POTUS for a pardon," Mitchell Epner, an attorney at Rottenberg Lipman Rich who was previously an assistant US attorney for the District of New Jersey, told Business Insider. "That is possible, but it would be very stupid on POTUS's part."

Cohen, who worked for Trump over the past decade, is the focus of an investigation in the Southern District of New York into whether he violated campaign-finance laws or committed bank fraud, wire fraud, illegal lobbying, or other crimes. The FBI seized roughly 4 million documents from the lawyer in April raids on his home, office, and hotel room.

In his interview with ABC News, Cohen finally broke with Trump, saying he would "put family and country first" when considering what he should do regarding that criminal investigation. When ABC's George Stephanopoulos pressed Cohen about his past vow to "take a bullet" for Trump, Cohen doubled down.

"To be crystal clear, my wife, my daughter, and my son and this country have my first loyalty," he said.

ABC News also reported that Cohen will soon end a joint defense agreement with the president, which allows lawyers of both parties to share information and documents. This echos a move from Trump's former national security adviser Michael Flynn just days before he reached an agreement with special counsel Robert Mueller.

Donald Trump. Associated Press/Evan Vucci Cohen hired a new attorney, Guy Petrillo, in June. Experts told Business Insider that he was the kind of lawyer a person would choose if he or she were seeking to cut a deal with prosecutors.

"Once I understand what charges might be filed against me, if any at all, I will defer to my new counsel, Guy Petrillo, for guidance," Cohen told ABC News.

Three options

As Epner laid out, the thing Trump most "has to fear" is Cohen testifying against him.

Cohen is protected by the Fifth Amendment from having to testify about anything at this point, Epner added, saying there are three possibilities for Cohen moving forward.

The first is that he does not get pardoned by Trump and does not cooperate with the government.

"Under these circumstances, the Fifth Amendment protection that he cannot 'be compelled in any criminal case to be a witness against himself' means that he could not be forced to testify about anything," Epner said. "This Fifth Amendment protection would continue even if Michael Cohen were to be indicted by the SDNY or special counsel Mueller's team. Even under these circumstances, POTUS would have nothing to immediately fear from Michael Cohen."

The second option is that Cohen "flips" and cooperates with the government, taking a plea agreement with the US attorney's office or Mueller, who is investigating Russian election interference and possible Trump campaign participation in it.

"Under these circumstances, Michael Cohen would waive his Fifth Amendment rights on all subjects related to either investigation," Epner said. "He would not be allowed to pick and choose the topics on which he would cooperate. He would be required to plead guilty to crime(s) that might lead to 10 years or more in jail. His sentencing would be delayed until the federal prosecutors had fully used him to cooperate on all matters."

"If they felt that he had failed to fully cooperate, they would have unlimited discretion to refuse to give him credit for cooperating and the district court judge would sentence him as if he had not cooperated," he continued. "If Michael Cohen has damaging criminal information about POTUS/Manafort/Jared Kushner/Donald Jr., this would be a disaster for them."

The third option features Trump pardoning Cohen to avoid that second scenario. Trump said last month it was too early to consider such a move.

"In that case, Michael Cohen would no longer have a Fifth Amendment right to avoid testimony," Epner said. "POTUS's pardon would cover past crimes, but it would not protect Michael Cohen against civil contempt for failure to testify before the grand jury. If Michael Cohen refused to testify before the grand jury, he could be jailed for the rest of the term of the grand jury (up to 18 months) until he testified."

"The Supreme Court held in 1925 that POTUS's pardon power does not cover civil contempt," he continued. "If Michael Cohen testified before the grand jury, POTUS would not know the content of that testimony. In addition, the only way that Michael Cohen would have criminal exposure after a pardon would be for perjury if he lied to the grand jury."

Because of that possibility, Epner said a presidential pardon for Cohen would actually "increase the risk to" Trump that Cohen would flip on him.

"POTUS has said and done many foolish things," Epner said. "Pardoning Michael Cohen would immediately go to the top of the list."