August is shaping up to be a blockbuster month as a series of primaries from Arizona to Kansas will start finalizing the shape of races in the critical contest for Congress.

The primaries are being dominated by intense partisanship on both sides, setting up what could be a midterm election shaped by sharply divergent policy stances and one where President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE will loom large.

Republican voters in Arizona and Wisconsin will pick their Senate nominees after brutal, costly primaries where support for Trump has become a key litmus test. Trump remains overwhelmingly popular among the Republican base, raising concerns about the emergence of ultra-conservative candidates who will struggle to win over general election voters.

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On the Democratic side, progressive candidates will battle for the nomination against more centrist candidates in places like Kansas, exposing two competing visions for the future of the party.

But Democrats, mindful of the need to compete in more conservative districts that will determine whether they can retake Congress, are also showing a more pragmatic side. Ohio will be a test case of this approach in a special House election on Aug. 7, with a Democratic candidate who has said he won’t support House Minority Leader Nancy Pelosi Nancy PelosiHoyer: House should vote on COVID-19 aid — with or without a bipartisan deal Ruth Bader Ginsburg lies in repose at Supreme Court McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE (D-Calif.).

Below is a breakdown of the big primaries and a special election to watch next month:

Aug. 7 (Kansas and Michigan primaries and Ohio special election)

Four states will hold pivotal House and Senate primaries, but the special election for retired Rep. Pat Tiberi Patrick (Pat) Joseph TiberiOhio New Members 2019 Many authors of GOP tax law will not be returning to Congress GOP Rep. Balderson holds onto seat in Ohio MORE’s (R-Ohio) seat will be the one to watch as Democrats assess their chances of taking back the House in November.

The once sleepy race between Republican state Sen. Troy Balderson and Democrat Danny O’Connor has gotten an injection of cash and is now seen as a “toss up” by The Cook Political Report.

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The GOP’s Congressional Leadership Fund went in early with more than $1.5 million in ads tarring O’Connor, a young Franklin Country recorder in charge of preserving real estate and property records, as a liberal with ties to Pelosi.

But O’Connor, like many other moderate Democrats, has said he won’t support Pelosi if elected. National Democrats also waded into the race last week with $240,000 in ad reservations and are hoping to turn O’Connor into another Conor Lamb, a young Democrat who defeated a more experienced politician in a Pennsylvania House special election in March.

A victory or close margin for Democrats would give them an uplifting shot in the arm before November in what has been a historically GOP district that Trump won by more than 11 points. Trump has endorsed Balderson, potentially motivating conservatives in a state the president won by 8 points.

Another race to watch on Aug. 7 is Kansas’s 3rd District, a must-win district for Democrats that Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE narrowly carried in 2016. Though the area tends to lean to the GOP, progressive candidates are competing against more centrist ones in the crowded primary.

Democrat Brent Welder, a former delegate for Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE’s (I-Vt.) presidential campaign, has gained some national star power, with help on the campaign trail from Sanders and Alexandria Ocasio-Cortez, who defeated Rep. Joseph Crowley (D-N.Y.) in a June primary.

Welder argues that Democrats haven’t been able to unseat Rep. Kevin Yoder Kevin Wayne YoderBottom line Amanda Adkins wins GOP primary to challenge Rep. Sharice Davids Sharice Davids to vote for Trump impeachment articles: 'The facts are uncontested' MORE (R-Kan.) because the party chooses moderates who haven’t staked out firm positions, and he is campaigning with progressive stances including calling for a single-payer health-care system.

Welder faces five other Democrats, including teacher Tom Niermann, a more centrist candidate who’s the top fundraiser, and Sharice Davids, a progressive backed by EMILY’s List who could be the first Native American woman elected to Congress.

The winner will face Yoder, a congressman who’s been endorsed by Trump. The race is listed as “lean Republican” by Cook.

Meanwhile, Michigan will have a bevy of primary activity in both Senate and House races.

Republicans Sandy Pensler, a businessman, and John James, a former Army pilot, are vying to take on Sen. Debbie Stabenow Deborah (Debbie) Ann StabenowOVERNIGHT ENERGY: Trump rollbacks could add 1.8 billion tons of greenhouse gas emissions over 15 years: analysis | Intensifying natural disasters do little to move needle on climate efforts | Experts warn wildfire smoke could worsen COVID-19 GAO report finds brokers offered false info on coverage for pre-existing conditions Democrats back away from quick reversal of Trump tax cuts MORE (D-Mich.). Stabenow is running for reelection in a state that Trump narrowly won, but Democrats are favored to hold it.

There are also wide-open Democratic primaries for competitive GOP-held seats that Democrats are heavily targeting in November, including Rep. Fred Upton Frederick (Fred) Stephen UptonOn Paycheck Protection Program, streamlined forgiveness is key Hispanic Caucus campaign arm endorses slate of non-Hispanic candidates Progressives soaring after big primary night MORE’s (R-Mich.) seat and Rep. Dave Trott David Alan TrottFormer GOP Michigan congressman says Trump is unfit for office Pro-Trump Republican immigrant to challenge Dem lawmaker who flipped Michigan seat Meet the lawmakers putting politics aside to save our climate MORE (R-Mich.).

Aug. 14 (Minnesota and Wisconsin)

Minnesota is poised to be one of the epicenters of the midterms, with an expansive battlefield that spans both Senate seats, the governor’s mansion and nearly half a dozen competitive House seats. The state will likely play a big role in which party controls the House.

Although Minnesota went to Clinton in 2016, Republicans believe they have a genuine shot at picking up seats, including the one being vacated by retiring Rep. Rick Nolan Richard (Rick) Michael NolanMinnesota Rep. Pete Stauber glides to victory in GOP primary Hold off on anti-mining hysteria until the facts are in Minnesota New Members 2019 MORE (D-Minn.). Nolan won reelection in 2016, even as Trump carried his district by more than 15 points.

When the seat opened up, Republicans quickly coalesced around one of their top recruits, retired police officer Pete Stauber. Trump campaigned with Stauber in June.

Meanwhile, Democrats face a wide-open primary among five Democrats in a seat they must protect. There’s no front-runner, but Democrats Joe Radinovich and Jason Metsa have emerged as the top two fundraisers.

In neighboring Wisconsin, Republicans will decide between state Sen. Leah Vukmir and Marine veteran and businessman Kevin Nicholson in the race against Sen. Tammy Baldwin Tammy Suzanne BaldwinSenators introduce bipartisan bill to mandate digital apps disclose country of origin Keep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser MORE (D-Wis.).

The Senate GOP primary has become bitter and costly, with billionaire donors lending a hand to both Vukmir and Nicholson. And, like other heavily contested GOP Senate primaries, support for Trump has played a big role.

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Nicholson, a first-time candidate, has run as a political outsider and had an early lead in primary polls. But he’s been dogged by his past as a former president of the College Democrats of America.

Vukmir, who has a conservative track record in the legislature, has gained some late momentum. The latest public poll shows her ahead by 2 points. She also won notable endorsements from the state GOP party and Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.).

The Senate race isn’t the only interesting primary in Wisconsin. The Democratic primary in the race to fill Ryan’s seat, which appeared all but settled months ago, has now become hotly contested.

Ironworker Randy Bryce came on the scene last June with a viral video that helped him become a fundraising powerhouse, bringing in more than $6 million.

But Bryce is facing a tightening primary against school board member Cathy Myers, which has gotten increasingly nasty. Myers is alleging that Bryce improperly used $7,000 in campaign funds to settle a personal legal scuffle. And Bryce has faced a barrage of bad headlines, most recently that he was arrested for driving under the influence two decades ago.

The Republican side is more settled, with Republican Bryan Steil, an attorney endorsed by Ryan, expected to win.

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Aug. 28 (Arizona and Florida)

Republicans hope to hold on to the seat being vacated by Arizona GOP Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE likely hinges on who wins the primary.

Establishment favorite Rep. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R) faces a tough challenge from former state Sen. Kelli Ward (R), an immigration hard-liner who has made the race largely about her unequivocal support for Trump. Still, McSally has led most recent primary polls.

In her Senate campaign, McSally has touted her work on immigration and strengthening border security, which are hallmark issues for Trump. But Ward has turned up the heat on McSally, accusing her of not backing the president in 2016 and being soft on border security.

Conservative hard-liner and former Maricopa County Sheriff Joe Arpaio is also running in the primary. The winner will face a formidable challenger, Rep. Kyrsten Sinema (D-Ariz.).

And in the race to replace McSally, former Rep. Ann Kirkpatrick Ann KirkpatrickArizona Rep. Tom O'Halleran wins Democratic primary Arizona Rep. Ann Kirkpatrick wins Democratic primary Cook shifts 20 House districts toward Democrats MORE (D-Ariz.) is looking to make a political comeback in a new district. Even with national Democrats’ support, Kirkpatrick faces a tough primary against Democrat Matt Heinz, who was the 2016 nominee. The eventual nominee is expected to face Republican Lea Marquez Peterson.

Florida will feature competitive primaries on both sides in the race to replace GOP Rep. Ileana Ros-Lehtinen Ileana Carmen Ros-LehtinenEx-Florida GOP congresswoman under federal investigation: report 'Trump show' convention sparks little interest on K Street Shalala to face Salazar in Florida rematch MORE, who is retiring. Democrats are expected to flip her district, which Clinton carried by 20 points.

Democrat Donna Shalala, a Health and Human Services secretary in former President Clinton’s administration, is the favored candidate to win the primary given her name recognition and fundraising. Democrat David Richardson, who’s been backed by Sanders-aligned Our Revolution, has gone on the attack, criticizing Shalala about mishandling a sexual assault case when she was president of University of Miami.