Donald J. Trump was indicted in Manhattan on Thursday, becoming the first American president, current or former, to be charged with a crime.

His indictment was handed up by a grand jury which has been hearing evidence about Mr. Trump for months. The Manhattan district attorney's office, which brought the charges, is focused on the former president's involvement in the payment of hush money to a porn star, Stormy Daniels, who said she had an affair with him. Michael D. Cohen, Mr. Trump's fixer at the time, made the payment during the final days of the 2016 presidential campaign.

The office of the district attorney, Alvin L. Bragg, issued a statement on Thursday evening saying that Mr. Trump had been indicted, and that his lawyers had been contacted to arrange a surrender. One of Mr. Trump's lawyers, Susan R. Necheles, said that Mr. Trump was expected to turn himself in and would likely face arraignment Tuesday, at which point the specific charges will be unsealed.

While the facts are dramatic and the indictment explosive, the case against Mr. Trump could hinge on an untested legal theory. A conviction is far from assured.