With their generally civil debates now over, the combative ad wars have begun as the three major GOP candidates pull out the stops to win their party’s nod on Aug. 7 to challenge U.S. Sen. Claire McCaskill, D-Mo., this fall.

Although three weeks are left, the ad attacks already have gotten particularly sharp between St. Louis businessman John Brunner and former state Treasurer Sarah Steelman.

The duo’s dueling has prompted some speculation that the other candidate in this political triangle – U.S. Rep. Todd Akin of Wildwood – might try to repeat his earlier success in laying low until near the end, then launching a TV blitz.

All told, eight Republicans are vying for their party’s nomination, but only Akin, Brunner and Steelman have been actively campaigning and raising money. How much each has raised, and already spent, will be known within days, when the trio file campaign-finance reports by Monday's deadline.

Brunner, who is largely financing his campaign himself, already has spent more than $2 million on TV ads. Akin last reported just under $2 million in the bank, almost twice Steelman’s tally of about $1.1 million.

On paper, the policy differences between the three are minor. All three espouse a philosophy of low taxes, less spending and fewer federal regulations.

All three are vocally opposed to the federal stimulus spending and the Affordable Care Act, the prime legislative achievement of President Barack Obama.

But to attract the support of the Republican base voters, all three know they need need to highlight any differences and any flaws in the opposition’s record -- and to appear the most conservative.

That’s where the endorsements and the attacks fit in.

First, a look at each of the trio, in the order they appear on the Aug. 7 ballot:

Akin, 65, is a former member of the Missouri House. He was elected to the U.S. House in 2000, with a narrow victory of fewer than 100 votes in a packed Republican field. His bills include a measure to keep “under God’’ in the pledge of allegiance. Akin frequently notes that he’s has been rated as the most conservative member of the Missouri delegation. He has been endorsed by former Arkansas Gov. Mike Huckabee, Minnesota congresswoman Michele Bachmann and Minuteman Project founder Jim Gilchrist, among others. (Click here for campaign launch.)

Steelman, 54, is a former member of the Missouri Senate and served as state treasurer from 2005-2009. Based in Rolla, Mo., she ran unsuccessfully for governor in 2008, angering the Republican establishment and has made a point of highlighting her renegade status. She also frequently notes her masters degree in economics. Steelman’s supporters include state House Speaker Steve Tilley, St. Charles County Executive Steve Ehlmann, commentator Dick Morris, Maggie's List, the Tea Party Express and state Sens. Jason Crowell, R-Cape Girardeau, and Kevin Engler, R-Farmington. (Click here for kickoff announcement.)

Brunner, 60, has never run for office before. He headed his family-owned business, Vi-Jon (which specializes in personal care products, such as Germ-X) from 1992 to 2006, when it was sold to a private equity firm.  Along with his business background, he often cites his status as a Marine veteran. Brunner’s supporters include U.S. Rep. Ron Johnson, R-Wis., as well as the Missouri Pork Association and the Missouri Soybean Association., and state Sen. Brian Munzlinger, chairman of the state Senate’s agriculture committee. (Click here for kickoff event.)

Dave Robertson, political science professor at the University of Missouri-St. Louis, says each candidate is targeting a different segment of Missouri’s Republican base.

“Brunner is appealing to the business wing of the party, while Steelman is focusing on the rural base,’’ Robertson said. “Akin is appealing to the ideological conservatives.”

The upshot, the professor added: “I don’t see a clear frontrunner in the group.”

That explains the candidates’ strategies in their latest ads.

George Connor, head of the political science department at Missouri State University in Springfield, Mo., said it was a "real smart move" for Akin to incorporate Huckabee into his commercials. Huckbee carried a number of rural Missouri counties in the state’s 2008 presidential primary.

"A Huckabee endorsement, a Huckabee appearance… That's going to diminish Steelman's support here in southwest Missouri,” Connor said.

Steelman’s latest ad has focused on Brunner and seeks to discredit his rural standing by focusing on a donation that his family’s foundation made to an animal-rights’ group several years ago. (Brunner said the donation was made by an adult daughter and doesn’t reflect his views.)

Brunner’s most recent ad has attacked both Steelman and Akin by singling out certain votes that he contends shows that both were big spenders, despite their rhetoric.

In Steelman’s case, Brunner highlights a 2003 vote in the General Assembly in favor of a bond issue that helped balance the state’s budget. (Steelman notes that most legislators backed the measure.) Brunner also targets Akin's votes for raising the federal debt ceiling. (Akin has replied that the increases were necessary to avoid cuts in the nation’s defense budget.)

Brunner also is expected to air an ad that continues his latest attack against Akin. In 2009, the congressman had been receptive to the idea of requiring people to purchase health insurance. Akin notes that many conservatives supported the idea at the time. He says he subsequently decided it was a “lousy idea’’ and never filed a bill.

Brunner, meanwhile, has come under fire over Vi-Jon’s recent rounds of layoffs and a drop in its credit rating. He has noted he hasn’t run the company since 2009.

Steelman’s allies include wealthy financier Rex Sinquefield, who is among the donors to a SuperPAC created to help her counter her rivals’ financial advantages. So far, the SuperPAC has yet to run any ads.

All three have been beset with some negative publicity – most recently, this week’s disclosures that all three have been late periodically paying their property taxes on houses, vehicles and, in the case of Brunner, his company plane.

The tax missteps could defuse similar controversies that have beset McCaskill for more than a year.   Because she has no primary opponent, McCaskill has been stockpiling her cash.

All the recent polls have shown her neck-and-neck, or trailing, all three of her Republican rivals.

Beacon reporter Jason Rosenbaum contributed information for this article.