“I’ve said it many times,” Mr. Mourdock said. “This is a historic time, and the most powerful people in both parties are so opposed to one another that one side simply has to win out over the other.”

That sort of talk has Democrats seething. “He says there’s a problem, Mourdock does, of too much bipartisanship and he can be counted on to obstruct,” Senator Charles E. Schumer of New York said on Tuesday. “Well, there are a lot of things wrong in Washington, but too much compromise is certainly not one of them.”

Mr. Mourdock said a pair of his earliest memories from his childhood in Ohio involved episodes that presaged his two careers. “I used to dig around the sandbox and pull out pieces of coal and show them to my mother,” he said, “and she used to say that’s how I must have known I was going to be a geologist.” The second, he said, was going to an elementary school in 1956 with his mother, “who held my hand and took me into a booth and pulled a lever for the president,” sparking an interest in politics.

He moved to Indiana for graduate school, and after receiving his master’s of science degree at Ball State University in 1975, he pursued geology, rising to vice president at the Koester Companies, a mining business in Evansville. But his interest in politics could not be contained.

Mr. Mourdock ran for the House in 1988, 1990 and 1992; he also failed in his 2002 bid for the nomination for Indiana secretary of state and in a 2004 race for the Vanderburgh County Council, the county’s fiscal body. He did get elected to the Vanderburgh County Commission, the executive branch, in 1994 and 1998, and won the state treasurer’s job in 2006. He was re-elected in 2010.

His name entered the national Republican discussion in 2009 when he became the country’s only government official to push back against the Obama administration’s auto bailout in court. Secured bondholders were forced to accept 29 cents on the dollar for their investments, which outraged Mr. Mourdock because three state funds — two managed by him — owned $42.5 million in Chrysler bonds.

Many lawmakers and business owners, some of them Republican, saw the challenge as folly since Indiana has so many autoworkers, the legal action was costly and a federal bankruptcy court and an appeals court rejected it.

Does he regret it now? “Absolutely not,” Mr. Mourdock said. “The law matters. And the fact was our retirees and teachers had their property stolen.”