(CNN) Former Republican Rep. Darrell Issa is expected to announce a bid to challenge Republican Rep. Duncan Hunter , who is facing federal corruption charges, according to a Republican familiar with Issa's thinking.

Issa is scheduled to hold a press conference at 8:30 a.m. PDT on Thursday, according to a news release.

Issa launched an exploratory committee in August to run for California's 50th Congressional District. In 2018, Issa said he would not seek reelection , after serving in Congress since 2000. He represented a Southern California seat that flipped to the Democrats along with a handful of others in 2018.

President Donald Trump last year nominated Issa to run the US Trade and Development Agency. Last week, a Senate hearing to consider Issa's nomination was postponed over how to handle questions raised in his FBI file.

Issa was chairman of the House Oversight Committee and had a reputation for being a conservative attack dog. He presided over contentious hearings into the attack on the US embassy in Benghazi, Libya, and on the Internal Revenue Service's targeting of conservative groups.

Hunter and his wife, Margaret, were indicted in 2018 for routinely using campaign funds for personal expenses and luxury family vacations. At the time, Hunter denied wrongdoing and shifted blame to his wife, who was at one point his campaign manager.

Hunter agreed to step down from his congressional committee assignments after the indictment, which came months ahead of the 2018 election. Hunter went on to win reelection after running a brazenly anti-Muslim campaign against his Democratic opponent.

Margaret Hunter pleaded guilty in June to conspiring with her husband to "knowingly and willingly" use more than $200,000 in campaign funds for personal use. She has agreed to cooperate with prosecutors , and is set to be sentenced on September 16. She faces a maximum of five years in jail.

Both Hunters previously pleaded not guilty to the federal charges. Hunter has said the charges were made in error, and Federal Election Commission reports show he repaid tens of thousands of dollars to his campaign account.

Hunter, a Marine Corps veteran who served three combat tours in Iraq and Afghanistan, has served in the House since his 2008 election, when his father retired and gave up the seat.

The congressman stoked a separate controversy when he strongly defended a Navy SEAL, Edward Gallagher, who was accused of war crimes. He was ultimately found not guilty of murder.

In defending Gallagher, Hunter said he posed for a photo with a dead enemy combatant and later said that as an artillery officer, his unit "killed probably hundreds of civilians." In a later interview with CNN he clarified he never targeted civilians.