INDIANAPOLIS — For roughly two decades, Indiana Treasurer Richard Mourdock toiled in the trenches of the state Republican Party, losing more races than he won. But along the way he made a name for himself among GOP loyalists, tirelessly working the fundraising circuit and building a strong network of ground-level support.

Now Mourdock, a 60-year-old geologist, is on the brink of handing the tea party its biggest victory of the 2012 elections: Sen. Richard Lugar's seat.

Mourdock "is the real deal. He didn't arrive in 2012 and try to develop a platform that would attract conservative voters to him. He attracts conservative voters to him because he's a conservative," said Mike Fichter, president of Indiana Right to Life, who cut his teeth in politics working on Mourdock's first unsuccessful run for Congress in 1988 and has repaid the favor by endorsing him over Lugar.

It was unthinkable just month ago that anyone could topple the six-term Lugar, let alone a little-known state treasurer. But like the marathon runner he is, Mourdock has steadily chipped away at Lugar's base with a successful campaign questioning the senator's residency and conservative credentials.

With the primary election on Tuesday, Mourdock appears to have evened the odds in what began as a David v. Goliath battle. Recent polls show momentum on Mourdock's side, and that has emboldened conservatives eager to shake up Washington.

"If we win here, we are going to win the election," said Josh Eboch, campaign manager for the tea party umbrella group FreedomWorks, as he rallied Mourdock supporters in a heavily Republican Indianapolis suburb on a recent Saturday afternoon.

At first blush, Mourdock seems an unlikely dragon slayer. The two-term state treasurer lacks the dashing presence of Florida Sen. Marco Rubio and the fiery rhetoric of tea party standard-bearers like Illinois Rep. Joe Walsh and Florida Rep. Allen West. Before his 2006 election as state treasurer, an office that carries little name recognition, Mourdock's only political experience consisted of two terms as a commissioner in the southern Indiana county that includes Evansville.

But the anti-incumbent sentiment that fueled the tea party's growth in 2010 and an unexpected court fight that thrust Mourdock into the national spotlight may change all that in Indiana, home to one of the nation's most organized tea party movements.

Mourdock, a former coal mining executive who enjoys tinkering with motorcycles and building race cars, has built a reputation as a GOP loyalist since that first run for Congress in 1988. He's a regular at party events ranging from large annual Lincoln Day dinners that are the staple of fundraising to picnics with as few as two people. He's so accustomed to delivering speeches about Abraham Lincoln and Ronald Reagan that he seldom needs notes.

"The first time we had him speak there was very, very little applause, and it was a speech about Abraham Lincoln, and we wondered: 'Did it bomb or what?' And then we realized that everyone was so reverent and spellbound that when it was over, it took a while for it to sink in," said Morgan County Republican Party Chairman Marty Weaver.

That helps illustrate the differences between Mourdock and Lugar, whom many county leaders say has ignored their fundraising dinners for years.

But while Mourdock's loyalty has kept him on the party's A-list, it was his role as the keeper of Indiana's bottom line that pushed him to the forefront.

In 2009, Mourdock launched what some saw as a quixotic bid to block the federal bailout of Chrysler, saying it violated bankruptcy law by giving unsecured creditors more than secured creditors, including some Indiana employee pension funds. He lost when the U.S. Supreme Court declined to rule on his objections, but won national recognition from conservatives looking for someone willing to challenge the status quo.

"I would just be another guy from Indianapolis coming to events like this, if it hadn't been for Chrysler," Mourdock told the party faithful during the Morgan County dinner. "Chrysler defined me as the guy from Indianapolis who will take a stand, the guy who will fight for something."

Yet his opposition to the Chrysler bailout is also his biggest weakness with voters who question the $2.8 million tab for legal fees in the case, as well as the threat the challenge posed to the auto industry, a backbone of Indiana's manufacturing-dependent economy.

"The guy was trying to take our jobs away," said Richie Boruff, president of the United Autoworkers Local 685 representing Chrysler workers in Kokomo, Ind. He's asking members to vote for Lugar, whether they're Republican or Democrat.

Even so, there's a sense that Mourdock is on the brink of something big. Even some longtime Lugar supporters are signaling it's time for a change.

"I think sometimes if you're in office too long, you think you become bigger than the office and you no longer represent Indiana. And in that regard, maybe Dick Lugar is an anachronism," said Lawrence County Republican Party Chairman Sam Bond, who first volunteered for Lugar as a student at Purdue University in 1976. Bond said he still respects the senator, but believes Lugar has become engulfed by a system that shuns change.

Hoosiers for Conservative Senate co-founder Monica Boyer said her group of tea party activists spent most of last summer focused on telling voters why Lugar should be kicked out of office, not on who should replace him.

That changed after their nominating convention last September. Mourdock attended; Lugar didn't.

"I went from being anti-Lugar to listening to what (Mourdock) was saying and being excited," Boyer said.

For his part, Mourdock calls Lugar "an absolute gentleman" and says he has voted for him in the past. But he also hopes this is the year that nice guys with long Washington records finish last.

"People at this level, they want to know a guy is going to take the fight for them," Mourdock said. "It's time to have some fight here and not just go along to get along."