Richard Mourdock, 2012's Low-Key Tea Partier

May 2, 2012 -- What do you get when the Tea Party's anger simmers away?

You get Richard Mourdock, the low-key fiscal conservative who's challenging Sen. Richard Lugar, the longest-tenured Republican in the U.S. Senate. The GOP senate primary in Indiana takes place May 8.

"I am a very even-keeled guy," Mourdock told ABC News in an April interview. "Mr. Lugar is trying to paint me as this wild-eyed Tea-Party guy. It's not like I just popped up like a morel mushroom in the spring of agitation."

Indeed he didn't. After a career in business, Mourdock was first elected state treasurer in 2006, debatably a better year for Democrats than 2008. Now, after that spring of agitation, he's been endorsed over Lugar by Sarah Palin, influential conservative blogger Erick Erickson, Congresswoman Michelle Bachman, D.C. conservative groups FreedomWorks and the Club for Growth, the American Conservative Union, the National Rifle Association, Citizens United, Tea Party Express, and Grover Norquist.

Mourdock is running, he says, because a handful of Indiana Republican State Committee members asked him to, a surprise to Mourdock given Lugar's long standing. "People started saying to me, 'It's time,'" Mourdock said. "I heard it many times: He has a Washington view and not a Hoosier view."

Lugar's supporters have sprung to his defense, most notable among them Gov. Mitch Daniels, the American Action Network, a D.C.-based 501(c)4 group founded by former Minnesota Sen. Norm Coleman and run by GOP fundraising luminary Fred Malek. Two super PACs have formed in 2012, one in D.C. and another in Sacramento, for the purpose of attacking Mourdock. The Young Guns Network, a 501(c)4 group formed by former aides to House Majority Leader Eric Cantor, is supporting Lugar with TV ads as part of a campaign on energy and conservation.

As a result, Indiana's Senate primary has become a proxy battle between the GOP's establishment and its Tea-Party wing. Last week, eight outside groups had spent nearly $2.2 million; since then, two more groups have gotten involved, and outside spending totals nearly $4.3 million.

Conservatives see Indiana as the latest battleground in the war over Republican Party identity, a chance to unseat one of the final old-guard senators who upholds such traditions as earmarks and working with Democrats. The race bears the mark of every Tea-Party-vs.-establishment primary in 2010: A conservative candidate arises, is backed by national groups (both the "grassroots" PACs and the TV-ad-funders), and Republicans enter an affair with a candidate deemed ideologically pure--one who may or may not change Washington.

Mourdock's supporters have outspent Lugar's $2.6 million to $1.6 million. As of March 31, Lugar had spent $5.1 million to Mourdock's $1.7 million. With news that Lugar's largest backer, the American Action Network, canceled $200,000 worth of air time, the possibility of Lugar's demise looks even more real.

With Mitt Romney as their presidential standard bearer, and with Sen. Orrin Hatch having learned from the downfall of last year's Tea-Party casualty Bob Bennett in Utah, Mourdock offers Tea Partiers their best chance for a high-profile primary coup in 2012.

One thing is certain: If Lugar loses, Maine's Susan Collins will be the only centrist, bipartisan Republican senator left.