Businessman Pat Maciariello announced Thursday that he is running to replace retiring GOP Rep. John Campbell in California’s 45th District, joining an already crowded GOP primary field in this strong Republican district.

Maciariello, a self-described political newcomer, joins state Sen. Mimi Walters, Orange County Supervisor John Moorlach and retired Marine Greg Raths in the GOP primary.

Walters is widely seen as the front-runner, earning endorsements from California Republican Reps. Ed Royce and Darrell Issa, among other local politicians.

The 45th District, based in Orange County, is one of the Golden State’s most strongly conservative districts. GOP presidential nominee Mitt Romney won the district in 2012 by 12 points.

The 45th District is rated a Safe Republican contest by Rothenberg Political Report/Roll Call.