[Update: The state charges against Paul J. Manafort have been dismissed by a judge in New York.]

The Manhattan district attorney’s office is preparing state criminal charges against Paul J. Manafort, President Trump’s former campaign chairman, in an effort to ensure he will still face prison time even if the president pardons him for his federal crimes, according to several people with knowledge of the matter.

Mr. Manafort is scheduled to be sentenced next month for convictions in two federal cases brought by Special Counsel Robert S. Mueller III. He faces up to 25 years in prison for tax and bank fraud and additional time for conspiracy counts in a related case. It could effectively be a life sentence for Mr. Manafort, who turns 70 in April.

The president has broad power to issue pardons for federal crimes, but no such authority in state cases. And while there has been no clear indication that Mr. Trump intends to pardon Mr. Manafort, the president has spoken repeatedly of his pardon power and defended his former campaign chairman on a number of occasions, calling him a “brave man.”

The office of the Manhattan district attorney, Cyrus R. Vance Jr., first began investigating Mr. Manafort in 2017 in connection with loans he received from two banks. Those loans were also the subject of some of the counts in the federal indictment that led to his conviction last year. But the state prosecutors deferred their inquiry in order not to interfere with Mr. Mueller’s investigation into Russian interference in the 2016 presidential election.