From a bitter Republican Senate showdown in Wisconsin to the race to fill former Sen. Al Franken Alan (Al) Stuart FrankenGOP Senate candidate says Trump, Republicans will surprise in Minnesota Peterson faces fight of his career in deep-red Minnesota district Getting tight — the psychology of cancel culture MORE's (D) term in Minnesota, Tuesday will feature a number of marquee primary races.

Voters will head to the polls in Wisconsin, Minnesota, Connecticut and Vermont to determine candidates for Senate, House and gubernatorial races.

Wisconsin will take a big part of the spotlight as a state that went Republican in the presidential election of 2016 for the first time in more than 30 years. Republicans Kevin Nicholson and Leah Vukmir have staged a bitter showdown in the GOP primary race to take on Democratic 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 in the fall.

Meanwhile, Democrats will decide their nominee to take on battle-tested Gov. Scott Walker (R), as the party looks to ride the momentum from recent wins in special elections for state legislative seats and a state Supreme Court seat.

And Minnesota has one of the largest battlefields of this year's election cycle, with both of its Senate seats up for grabs, including Franken's old seat, along with a governor’s race and a number of House races that could very well help decide who takes over the chamber in November.

Here are the key races to watch on Tuesday:

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All-out Republican brawl to take on Baldwin

Wisconsin’s GOP primary resembles many other Senate primaries that have played out this year: a costly, bitter fight that has hinged on how closely Republicans can associate themselves with President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE - even if it’s a primary where Trump has actually stayed out.

Neither candidate, however, fits the typical mold of a Trump Republican in a race that is dead-even according to the latest polling.

Nicholson, a first-time candidate and Marine veteran, has fashioned himself as an outsider. But he’s been haunted by his past as a Democrat, which Vukmir has used against him.

Meanwhile, state Sen. Vukmir is endorsed by 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, which has opened her up to attacks from Nicholson that she’s part of the establishment. But Vukmir has also come under attack over comments she made that were critical of Trump during the 2016 primaries.

Both Nicholson and Vukmir initially backed other presidential candidates, but are now fighting to see who is President Trump's biggest supporter.

Republicans are hoping that whoever emerges as the winner will have the support of the other, as the party seeks to avoid a repeat of 2012 when a messy primary contributed to a loss against Baldwin.

The race could be a hard one for Republicans, with the seat rated as "likely Democrat" by The Cook Political Report. And both Nicholson and Vukmir have under half a million dollars in the bank, well below Baldwin’s $7.2 million war chest.

'Iron Stache' in race to replace Speaker Ryan

Ironworker Randy Bryce was long viewed as the front-runner in the Democratic primary for House Speaker Paul Ryan’s (R) seat in Wisconsin's 1st District. But the spirited primary has become a bit of a nail-biter heading into Tuesday.

Bryce, the mustachioed 53-year-old known as “Iron Stache,” burst onto the national scene with a campaign announcement video that went viral last summer. That attention led to prolific fundraising, with Bryce raising more than $6.2 million since he announced.

But "Iron Stache" is facing a heated challenge from Janesville school board member Cathy Myers, who’s seen a late boost in momentum. There’s limited polling in the race, but a survey from a GOP super PAC found them in a dead heat.

Bryce and Myers are largely aligned in their policy proposals, with a similarly progressive agenda, though Bryce earned Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE’s (I-Vt.) endorsement late last year.

Bryce has endured a spate of negative headlines, which include revelations that he didn’t pay child support until after his campaign announcement, as well as past arrests related to driving under the influence and marijuana possession — all things he’s apologized for.

Ryan’s departure also attracted a crowded GOP primary. But Bryan Steil, a former Ryan aide who’s endorsed by the speaker, has been the overwhelming favorite.

The race has been rated as "lean Republican" by Cook.

Republicans’ best pick-up chances in Minnesota

Two open-seat races in rural Minnesota districts give Republicans some of their best shots at picking up seats this election cycle in their quest to keep a majority in the House.

Rep. Tim Walz Tim WalzGOP Senate candidate says Trump, Republicans will surprise in Minnesota Presidential race tightens in Minnesota as Trump plows resources into state National Guard activated in Minneapolis after homicide suspect's reported suicide MORE (D-Minn.), who’s now running for governor, won reelection by less than a point in 2016, in a district that Trump carried by nearly 15 points. And 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.), who’s also vacating his seat, won reelection by just a point, while Trump carried the district by nearly 16 points.

Republicans smell opportunity in both races.

In the GOP primary for Walz’s seat, Republicans will see a familiar name on the ballot: Jim Hagedorn, a businessman who’s making his fourth run in Minnesota’s 1st District.

Hagedorn came close to unseating Walz in 2016. Despite snagging the state party’s endorsement, he is facing a fierce competitor in Republican state Sen. Carla Nelson. She’s gotten support from some big-name donors as well as a last-minute endorsement from the National Rifle Association.

Meanwhile, on the Democratic side, Iraq War veteran Daniel Feehan is viewed as the overwhelming favorite going into Tuesday in the race to replace Walz.

The picture is clearer in the Republican primary to take Rep. Nolan's open seat in the state's 8th District. Republican Pete Stauber, a retired police officer and hockey player, is a prized GOP recruit who’s been able to skate by without a competitive primary.

But the Democratic side is more crowded, in a race where the national party has stayed out. Democrat Joe Radinovich, a former state legislator who was Nolan’s campaign manager in 2016, is the top fundraiser among the Democrats and the only one up on the airwaves.

Some of the other Democratic candidates include state Rep. Jason Metsa, North Branch Mayor Kirsten Kennedy and former TV news anchor Michelle Lee.

The special election to take on Sen. Franken's successor

Sen. Tina Smith Tina Flint SmithThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Credit union group to spend million on Senate, House races Health officials tell public to trust in science MORE (D-Minn.), a former lieutenant governor, was appointed late last year to replace Sen. Al Franken, who resigned amid allegations that he kissed and groped women without their consent.

Smith faces a long-shot primary challenge from Richard Painter, a former Republican who served as President George W. Bush’s ethics counsel.

On the Republican side, state Sen. Karin Housley is expected to prevail against two little-known rivals.

A recent poll showed a tight race between Housley and Smith, in a race that would feature two female candidates in what is seen as "the year of the woman." But Democrats are still expected to keep the seat in November, in a special election that will serve the remaining two years of Franken's term.

Dems pick nominees in critical Wisconsin, Minnesota gov races

Winning, or holding, governorships in states like Wisconsin and Minnesota will be critical two years before the next reapportionment process is scheduled to start with the 2020 Census.

In Wisconsin, eight Democrats are vying for the right to face off against Walker in the fall. The crowded field has kept many donors on the sidelines, but the state Democratic Party has hired a strategist to line those donors up to cut checks to the winner hours after the polls close.

State Superintendent of Public Instruction Tony Evers (D) leads in public polls, and those same polls show Evers leading Walker.

In a sign of just how seriously Democrats take their chances of beating Walker, the Democratic Governors Association has blocked off $4 million in television airtime to prop up their nominee as he or she restocks their campaign war chest.

In neighboring Minnesota, Attorney General Lori Swanson (D) made a late entrance into the race to replace term-limited Gov. Mark Dayton (D). Swanson is running neck and neck with Rep. Tim Walz, the congressman long seen as the front-runner, while party-endorsed state Rep. Erin Murphy (D) trails in third place.

A few months ago, it seemed certain that the Democratic nominee would face off against Dayton’s predecessor, former Gov. Tim Pawlenty (R).

But Pawlenty faces an unexpectedly tough challenge in the Republican primary from Hennepin County Commissioner Jeff Johnson (R), who lost to Dayton in 2014. Johnson has cast himself as a candidate in the mold of Trump, while painting Pawlenty as an establishment politician.

The return of Ned Lamont in Connecticut

Twelve years ago, businessman Ned Lamont stunned political observers when he rode a wave of discontent over the war in Iraq to beat Sen. Joe Lieberman in the Democratic primary. Lieberman came back to win reelection as an independent, but Lamont didn’t go away — and now he’s likely to capture the Democratic nomination for governor.

Lamont faces convicted felon and Bridgeport Mayor Joe Ganim (D) in Tuesday’s Democratic primary, although most of the state’s political elite has lined up behind the businessman.

He would face the winner of a crowded Republican field led by Danbury Mayor Mark Boughton (R). Two other candidates are spending their own fortunes introducing themselves to voters: Hedge fund manager David Stemerman, who has spent $6 million on his own campaign, and businessman Bob Stefanowski, who has dropped $2.9 million on his own behalf.

They are running to replace Gov. Dan Malloy (D), who is stepping down next year after two rocky terms. In what looks like a good year for Democrats, Connecticut gives Republicans a reason to be optimistic after they have made inroads in the ordinarily blue state.

Northeastern Republicans holding their own in Vermont

Vermont Democrats are likely to make history Tuesday if they vote for Christine Hallquist, a former CEO of the state’s electricity co-op who would be the first transgender woman to win a major party’s gubernatorial nomination.

But Hallquist faces a tremendous uphill fight in November against Gov. Phil Scott (R), who is running for a second term.

Scott won office with 53 percent of the vote in 2016, one of the very few Republicans who won statewide office in a state Clinton carried that same day. He has cast himself as a different kind of Republican, more in the mold of other moderate GOP governors serving in blue states.