Mr. McCarthy, the majority leader, is also expected to be confronted on his ability to corral the most conservative Republicans in the House, who pressured Mr. Boehner to step down.

Mr. McCarthy is from Bakersfield, a bastion of California Republicanism about 100 miles north of Los Angeles. A graduate of California State University, Bakersfield, Mr. McCarthy was active in the Young Republicans. He worked as district director for Representative Bill Thomas, who became chairman of the powerful Ways and Means Committee.

When Mr. Thomas retired in 2006, Mr. McCarthy, who was serving in the California State Assembly, ran for his seat. Mr. McCarthy rose quickly through the Republican ranks in part because of his fund-raising skills. Along with Representatives Eric Cantor of Virginia and Paul D. Ryan of Wisconsin, Mr. McCarthy was part of a group of so-called Young Guns in 2010 who were crucial to Republicans’ regaining the majority. During that cycle, Mr. McCarthy was head of recruiting for the National Republican Congressional Committee, which provides another base of support for him among the rank and file.

The No. 2 Republican in the House is often such a shoo-in for the speaker’s job that the fight for that lower post generates the fiercest competition among lawmakers climbing the ranks.