Former congressman Darrell Issa (R-Calif.) announced Thursday that he is launching a primary challenge to Rep. Duncan D. Hunter (R-Calif.), who has been accused by prosecutors of using campaign funds to help facilitate extramarital affairs.

Issa, who represented a neighboring San Diego-area congressional district for 18 years before retiring in January, created an exploratory committee last month to look at a race against the embattled Hunter.

“I will be the next congressman from the 50th Congressional District,” Issa said during a news conference Thursday in El Cajon, Calif. “I have the history, the skills, the seniority and the capability to hit the ground running, not just for this district but for California.”

Issa, a former House Oversight and Reform Committee chairman, was nominated last year by President Trump to lead the U.S. Trade and Development Agency, but his nomination has stalled in the Senate.

Issa built a national profile as the chief congressional antagonist to President Barack Obama and his administration during his tenure as top Republican and then chairman of the Oversight panel between 2008 and 2015. He later targeted former secretary of state Hillary Clinton, as she prepared to seek the presidency, over her response to the deadly 2012 attacks on Americans in Benghazi, Libya.

But Issa’s hold on his district became increasingly tenuous, and he barely fended off a Democratic challenger in 2016. When he announced plans to retire in early 2018, Issa said he was “looking forward to another chapter in my life.”

Former San Diego city councilman Carl DeMaio is also running for the Republican nomination. In a statement, his campaign spokesman, Dave McCullough, took aim at Issa’s record and said the former congressman “epitomized what is wrong with career politicians when he fled his own district rather than fighting for it and his constituents.”

Hunter and his wife, Margaret, were charged last year with using more than $250,000 in campaign funds to pay for family vacations, theater tickets and other personal expenses. In a new filing in June, federal prosecutors alleged that Hunter used campaign money to fund trips, dinners and drinks with other women with whom he was romantically involved.

Hunter has accused prosecutors of pursuing him for political reasons. He has continued serving in Congress and won reelection last year despite being charged.

Democrat Ammar Campa-Najjar, who lost narrowly to Hunter last year, is also pursuing a bid for the seat.

Felicia Sonmez, Mike DeBonis and Matt Zapotosky contributed to this report.