WASHINGTON — Representative Jason Chaffetz of Utah admits he is not the best candidate to become speaker of the House. He fully expects to lose when his Republican colleagues pick their nominee on Thursday. But opportunity for Mr. Chaffetz is like the scent of an airport Cinnabon, and he has a habit of racing to its smell.

So it was last week that Mr. Chaffetz helpfully informed his “good friend,” Representative Kevin McCarthy of California, that he would challenge him in the race to replace Speaker John A. Boehner. He pointed out that Mr. McCarthy, while the clear favorite of a majority of House Republicans, would most likely fail to get the 218 supporters needed on the House floor to become the next speaker.

“Ten days ago, I didn’t think I’d do this,” Mr. Chaffetz (pronounced CHAY-fets) said in an interview in his Capitol Hill office-cum-hotel room, where he also sleeps, made cozy by some throw pillows decorated with the famous Utah honeybee. “There are very few opportunities to do this,” he said. “You have to be comfortable with losing. I am.”

When Mr. McCarthy’s wall of support began to crack last week — after he suggested on Fox News that the House committee investigating the 2012 terrorist attack in Benghazi, Libya, had a political aim to drive down support for Hillary Rodham Clinton — Mr. Chaffetz, 48, ran a play he has mastered over the last decade: Seize the moment, talk about love of country, and prepare for the live shot.