House Judiciary Chair U.S. Rep. Jim Jordan on Thursday issued a subpoena to ex-prosecutor Mark Pomerantz—an apparent escalation of the Republican probe into Manhattan District Attorney Alvin Bragg’s investigation of former President Donald Trump.

Pomerantz previously served as a Special Assistant DA to the office, but resigned soon after Bragg came into office. He went on to write a book criticizing Bragg for his failure to bring a criminal case against the former president.