Andrew Bailey, FBI co-deputy director who was once widely viewed as a potential successor to FBI Director Kash Patel, is resigning, he announced Monday.

His resignation takes effect Oct. 2, multiple sources said. In an email to agents Monday morning and a post on X about his resignation, Bailey cited family reasons. In an X post, Patel thanked Bailey for “his fantastic contribution instituting critical reforms.”

Bailey was previously the Missouri attorney general who was brought in to help ease reported tensions between former Attorney General Pam Bondi and former FBI Deputy Director Dan Bongino. He was elevated to co-deputy, a position that had always been filled by a career staffer. It marked the first time that the job was split between two people.

From the outset, Bailey’s relationship with Patel was troubled. Initially, Bailey was not invited to meetings, according to two sources familiar with their dynamic, with one adding that Patel instructed staff to refer to him as director, to Bongino as deputy director and Bailey as co-deputy director.

The sources added that Patel consistently kept Bailey at arm’s length and cut him out of meetings the deputy FBI director should attend because Bailey was constantly flagging things that were unconstitutional.

Bongino left the FBI in January. There is still another FBI co-deputy, Chris Raia, who was formerly the assistant director in charge of the bureau’s New York City Field Office.

Bailey’s resignation comes shortly after two agents who oversaw counterterrorism at the Washington Field Office were demoted after White House deputy chief of staff for policy Stephen Miller and his wife, Katie Miller, complained that the FBI was not doing enough to investigate alleged threats against them. 

Stephen and Katie Miller didn’t request that anyone be fired over the handling of threats against Katie Miller, but FBI officials chose to reassign some FBI personnel, according to two sources familiar with the matter. 

Last fall, the Millers moved into military housing after a local activist protested Trump administration policies outside their home and encouraged protesters to call for a congressional investigation into Stephen Miller. NBC News first reported Bailey’s resignation.

The FBI has not responded to a request for comment, and the White House has not responded to a request for comment.

Sara Cook and Julia Kimani Burnham contributed to this report.