LOS ANGELES (AP) — George Papadopoulos, a former Trump campaign aide who was a key figure in the FBI’s Russia probe, is running for the U.S. House seat left vacant by Democrat Katie Hill.

Papadopoulos filed paperwork Tuesday with the Federal Election Commission.

Hill announced her resignation Sunday amid an ethics probe into allegations she had a relationship with a congressional staff member.

The FBI probe into ties between Russia and the Trump campaign began after revelations that Papadopoulos had learned Russia had thousands of stolen emails related to Hillary Clinton.

Papadopoulos eventually pleaded guilty to lying to the FBI and cooperated in special counsel Robert Mueller’s investigation. He was sentenced to 14 days in prison.

He joins a field with at least three other Republican candidates and one Democrat.