Missouri’s hotly contested Republican Senate primary will be decided on Tuesday, with major implications for the fall campaign against embattled Sen. Claire McCaskillClaire McCaskillSenators question need for HHS cyber office Overnight Cybersecurity: Obama DHS chief defends Russian hack response | Trump huddles on grid security | Lawmakers warned about cyber threat to election systems We must protect our most vulnerable from financial fraudsters MORE (D) — and control of the Senate.

Wealthy businessman John Brunner is the slight favorite heading into the closing days of the primary, but former state Treasurer Sarah Steelman and Rep. Todd Akin have maintained their bases of support, and polls show any of the three has a chance to pull off the victory.

The race is the marquee matchup in a string of competitive primaries in Missouri and Michigan on Tuesday.

A poll released by the Democratic firm Public Policy Polling on Monday showed Brunner in the lead with 35 percent, followed by Akin at 30 and Steelman at 25. All three Republican campaigns told The Hill that Brunner has held a slight lead in their internal polling but that the race was a bit closer than PPP’s results and could easily be won by any of the candidates.

Democrats have made it clear they prefer to face Akin. McCaskill has already run ads blasting all three — but the ads against Akin described him only as the “true conservative" in the race and say he’s a “crusader against bigger government” — hardly a damning offense in a Republican primary.
While McCaskill’s campaign denies she has a preference in the race, Republicans tracking her ad buys in the state say that nine out of 10 ads have been those describing Akin as a conservative, while only 5 percent have been the anti-Steelman and anti-Brunner ads. Majority PAC, a Democratic super-PAC, has been running ads against all three candidates at the same rate, although they, too, don’t attack Akin on issues that could hurt him with Republican primary voters.

Control of the Senate could be at stake. Republicans only need a net gain of four seats (if President Obama wins reelection) to win the upper chamber, and Missouri is one of their leading targets. The GOP has spent more than $15 million to date against the first-term senator.
Brunner, a wealthy businessman, had held a more sizable lead in the primary earlier this summer, largely because he’d used nearly $8 million of his personal fortune to start running ads long before the other candidates could afford to go on air. 

His campaign pointed out that a super-PAC with ties to Senate Majority Leader Harry ReidHarry ReidDems see surge of new candidates Dems to grind Senate to a halt over ObamaCare repeal fight GOP fires opening attack on Dem reportedly running for Heller's Senate seat MORE (D-Nev.) and the national party has aired ads attacking the businessman.

"Over the course of the last three and a half weeks, McCaskill, Reid and the [Democratic Senatorial Campaign Committee] have spent over $2 million attacking John Brunner and he's still leading in the polls. He's taking bombardment from all sides, from the Democrats and from Steelman," Brunner spokesman Todd Abrajano told The Hill in explaining why the race had tightened. "I'm feeling very good about where we're at."

But two endorsements have reshaped the race.
Former Arkansas Gov. Mike Huckabee (R), who remains immensely popular with the state’s conservative Christian voters, backed Akin earlier this year, and the congressman has run ads featuring Huckabee in recent weeks. All campaigns say the Huckabee endorsement helped Akin close what had been a large double-digit lead for Brunner coming into July.
Steelman’s endorsement made even bigger waves with the conservative grass roots. Former Alaska Gov. Sarah Palin (R) threw her support to Steelman two weeks ago, and spent Friday stumping with her.

All the campaigns concede Palin’s endorsement has given Steelman a big lift, and while Brunner and Akin insist she’s still in third place, the wind seems to be at her back.
Brunner also has had support from the Chamber of Commerce, which has attacked Steelman in ads. A super-PAC supporting Steelman has spent heavily on her behalf in rural southwestern Missouri, where her political base is.

“I don't know that anyone's walking away with this,” said Steelman spokesman Patrick Tuohey. “It's all pretty tight, and we just all have to focus on turning our voters out.”
Brunner’s and Akin’s campaigns both concurred.
“We're feeling very good about going into tomorrow. I know Steelman has had a good bit of movement because of Gov. Palin coming in, but I haven't seen any polling that shows her catching up completely,” said Akin spokesman Ryan Hite. “A month ago I would have said it was a two-person race, but I know she has a lot of traction right now — she's closed that gap pretty considerably.”
There is little daylight between the candidates on the issues, although Brunner has attacked Akin for supporting earmarks. Brunner has touted his lack of political experience and promised to be a “citizen legislator,” while Akin had touted his conservative record in Congress and Steelman has promised to “kick down the door” of the Republican establishment and cut spending in Washington.
McCaskill is likely to have a tough fight on her hands no matter who wins the primary. She hasn’t cracked 50 percent support in public polls against any of them in more than a year, and most recent polling of the race shows her trailing all three of her opponents.
The once-purple state has trended Republican in recent years in a big way, and McCaskill is closely tied to Obama, who is deeply unpopular in parts of Missouri.
McCaskill’s campaign insists it can win a race against any of her opponents. Her early ads show how she plans to attack them: She has blasted all three for backing Rep. Paul RyanPaul RyanRyan reminds lawmakers to be on time for votes Lawmakers consider new security funding in wake of shooting Paul Ryan: ‘Beautiful day’ to catch up with Bono MORE’s (R-Wis.) plan to privatize Medicare and opposing the bipartisan farm bill that was recently blocked in Congress. She’s also attacked Akin for his comments that “Social Security has been a terrible investment” and that he “doesn’t like” it, as well as his support for earmarks (which McCaskill has fought to end). Brunner will face attacks on his business dealings.
Tuesday will also end the career of at least two Democratic House members. Rep. Lacy Clay (D-Mo.) is expected to win his primary against fellow Rep. Russ Carnahan (D-Mo.), who decided to run against Clay in a newly drawn district that is mostly Clay’s territory. A poll released Tuesday showed Clay with a 21-point lead in the race. Rep. Gary Peters (D-Mich.) also has the edge over Rep. Hansen Clarke (D-Mich.) in a newly drawn Detroit-based district: Two recent polls had him with large double-digit leads.
Former Rep. Pete Hoekstra (R-Mich.) is expected to best businessman Clark Durant (R) in the state’s GOP Senate primary. Whoever wins will begin the general election against Sen. Debbie StabenowDebbie StabenowNo certainty on cost-sharing payments to insurers Dems express concerns about Trump's proposed rural development cuts Trump, Clinton campaign aides launch their own bids MORE (D-Mich.) as a major underdog.

Two other primaries could affect House control.

An establishment Republican is trying to win a write-in race against a Tea Party insurgent in a GOP-leaning district previously held by Rep. Thaddeus McCotter (R-Mich.). Democrats are hopeful that if the Tea Partier wins they can pick up the seat.

And Democrats have a competitive primary of their own to take on Rep. Justin AmashJustin AmashRepublicans slam Trump’s new policy toward Cuba Kids shouldn't be charged as sex offenders Dem: Disrespect for rule of law by Trump administration 'off the charts' MORE (R-Mich.). They are hopeful that if the more centrist candidate wins, he can put the seat in play this fall.