The U.S. Attorney’s Office for the Southern District of New York is reportedly preparing criminal charges against President Donald Trump’s former campaign chairman Paul Manafort. The effort, which will likely be challenged, is to ensure Manafort still faces prison time in the event of a presidential pardon.

Though the president hasn’t made any remarks publicly in regards to granting Manafort a full pardon, he has repeatedly asserted his right to do. Though Trump has the ability to grant pardons on federal crimes, such as Manafort’s sentence recommended by the special counsel, he does not have the authority to overturn a conviction in state court.

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Manafort who’s nearly 70, faces upwards of 25 years in prison and is expected to be sentenced next month for two federal cases brought forth by the special counsel’s office and which includes an array of charges ranging from tax and bank fraud to additional time for conspiracy counts, and repeatedly lying to prosecutors.

The Manhattan District Attorney’s Office reportedly began investigating Manafort in 2017, when it became suspicious and opened an inquiry into two bank loans he’d received. However, it was put on hold to avoid interference with Special Counsel Robert Mueller III investigation into Russian meddling during the 2016 presidential election.

Both of the loans he’d received were the subject of some of the counts alleged by Manafort in the federal indictment in the lead up to his conviction in 2018.

Any charges brought forward by the Southern District Attorney’s Office would likely be challenged by the former campaign chairman’s defense team on the grounds of double jeopardy, which the law in the State of New York includes stronger protections for than that of the nations own constitution.