In a volatile and heated campaign, the GOP chose Akin to take on McCaskill over former state treasurer Sarah Steelman and wealthy businessman John Brunner. Akin won 36 percent of the vote, with Brunner taking 30 percent and Steelman 29 percent.
Unlike in other recent key Republican Senate primaries, including races in Texas and Indiana, none of the three candidates were traditional establishment picks, and each had sought to lay claim to the mantle of small government outsider.
But in the final days of the race, they had sought to appeal to different splinters of the conservative electorate.
Akin received a late surge of support from evangelicals, impressed by his close ties to former Arkansas governor Mike Huckabee and his long-standing support for conservative social causes.
In a speech to supporters Tuesday night, Akin prominently thanked Huckabee for his efforts, just after offering gratitude to God.
“The choice is clear in November,” he said, according to prepared remarks. “The big-spending, budget-busting, job-killing liberal or the less spending, balanced budget, job-creating conservative?”
McCaskill appeared to be rooting for Akin as well. She ran ads clearly designed to boost his chances — criticizing him as the most conservative candidate in a backhanded attempt to appeal to a Republican electorate looking for the most right-leaning choice, an unusual strategy that could have boosted his numbers.
A race against Akin will let McCaskill highlight his long record in Congress, including support for earmarks and recent votes for the controversial Republican budget written by House Budget Committee Chairman Paul Ryan (Wis.).
Brunner, a first-time candidate who spent more than $7.5 million of his own money, positioned himself as a Mitt Romney-style job creator, basing his campaign on his years as head of successful health-care product manufacturer Vi-Jon.
Steelman received late support from former Alaska governor Sarah Palin, who has had the golden touch this year — every candidate she has endorsed has won his or her primary. Palin invested considerable energy in the race.
But the real question Tuesday was whether the identity of the Republican candidate would matter much to the outcome in November of a race that will test McCaskill’s folksy and tireless campaigning style.
National Republicans have long believed that she would be vulnerable to any challenger, after voting in favor of Democratic health-care reform and the economic stimulus plan. They think she took a hit as well when it was revealed in 2011 that she had not paid property taxes on a private plane. She later paid the taxes and sold the plane.
“Senator McCaskill is the most endangered incumbent in either party, for the simple reason that her voting record is wildly out of step with the voters of Missouri,” said Brian Walsh, a spokesman for the National Republican Senatorial Committee.
McCaskill has countered that she could beat any of the three — promising that Missouri’s independent voters would conclude that the GOP candidates were too conservative and uncompromising to solve problems in Washington.
“Three of a kind,” she termed them last week.
Still, McCaskill is widely believed to face an uphill climb in a race considered a model for outside spending by super PACs.
Outside groups have already spent an estimated $15 million in the state, most of it to paint McCaskill as a lackey of President Obama who is out of step with her constituents. She has waged an unusual assault against such spending that has appeared to do little to discredit the attacks.
“She’s working against a strong head wind at this point — everyone thinks the odds are with her opponent,” said David Robertson, a political science professor at the University of Missouri at St. Louis. “She’s going to be the underdog” on Wednesday, he said.
Democrats promise that the fundamentals of the race will shift on Wednesday, when McCaskill will cease shadow-boxing against outside groups and begin to focus on defining Akin.
“All three of these tea partyers have avoided scrutiny in part because of the primary,” said Matt Canter, a spokesman for the Democratic Senatorial Campaign Committee.
Also Tuesday, Republicans in Michigan chose former congressman Pete Hoekstra to take on Democratic Sen. Debbie Stabenow. Polls have shown the Republican will have ground to make up to win in November.
Two Democratic House members, meanwhile, lost their seats in primaries Tuesday as a result of rare intraparty battles made necessary by redistricting.
In Michigan, two-term Rep. Gary Peters (D) defeated freshman Rep. Hansen Clarke (D) in Detroit.
In a St. Louis race that pit two scions of well-known Missouri families against each other, Rep. William Lacy Clay (D) defeated Rep. Russ Carnahan (D).
And in Michigan, Rep. John Conyers Jr. (D), who has served in the House since 1965, fended off a challenge from state Sen. Glenn Anderson, his most formidable challenger in 20 years.