Katie Porter will face an Orange County G.O.P. stalwart, Scott Baugh, in the fall.

Scott Baugh, the former leader of the California Assembly, fended off a crowded Republican field on Tuesday to earn the right to challenge Representative Katie Porter, a Democratic star, in November.

The newly drawn 47th District of California leans slightly Democratic, but in a difficult year for President Biden’s party, Republicans would relish dimming Ms. Porter’s shine. Since she took her seat in the former Republican stronghold of Orange County in 2018, Ms. Porter has emerged as a powerhouse fund-raiser and a popular figure for the activist left.

Democratic officials widely see her as an heir to the Senate seat now held by Senator Dianne Feinstein, who is not expected to seek re-election in November 2024, when she will be 91. A loss now would complicated Ms. Porter’s path.

Mr. Baugh is the essence of the Orange County Republican establishment, having once headed the party in the county.

With more than $1 million in his campaign accounts, he heads toward November in a respectable position. But his cash on hand pales in comparison with Ms. Porter’s $18 million in a widely watched race is likely to be expensive.