A former Atlanta-area U.S. attorney testified to lawmakers on Wednesday that he abruptly resigned from his post in January after former President Donald Trump grew frustrated with him over his refusal to back election fraud claims in the state.

Byung Pak, who served in the Northern District of Georgia after his appointment by the former president, outlined the reason for his departure with the Senate Judiciary Committee during three hours of closed-door testimony, according to the New York Times, citing a person familiar with the remarks. He said he resigned after being informed by Justice Department officials Trump intended to fire him.