A pivotal showdown for the Republican gubernatorial nomination in battleground Wiscons takes center stage on Tuesday, as four states from New England to the upper Midwest hold primaries.

The fight for Wisconsin’s GOP gubernatorial nomination between former conservative Lt. Gov. Rebecca Kleefisch and businessman Tim Michels is the latest test of GOP clout between former President Donald Trump and former Vice President Mike Pence, one-time running mates who could potentially face-off against each other for the 2024 Republican presidential nomination.

Kleefisch and MIchels are the front-runners in a field of four Republican candidates that also includes state lawmaker Timothy Ramthun. The GOP primary winner will face off in November with Democratic Gov. Tony Evers, who faces no primary challenge but who’s being heavily targeted by Republicans as he seeks a second term.

Michels is a multimillionaire owner of a construction company who in early June was endorsed by Trump. Two weeks ago, Pence once again broke with his former boss as he backed Kleefisch. 

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Rebecca Kleefisch teams up with former Vice President Mike Pence

Former Vice President Mike Pence and GOP gubernatorial candidate and former Lt. Gov Rebecca Kleefisch of Wisconsin participate in a round table discussion. (AP Photo/Morry Gash, File)

"There is no candidate for governor in America that is more capable, more experienced or a more proven conservative than Rebecca Kleefisch," Pence said as he teamed up with the former lieutenant governor at a campaign stop in suburban Milwaukee on Wednesday.

And Kleefisch touted that she's "tested and proven and ready to go," and that she's "the one who has won statewide four times."

Two days later, as he headlined a rally for Michels in Waukesha, Trump charged that "Rebecca Kleefisch does not have what it takes to beat Tony Evers… He's going to win if he runs against Rebecca."

KLEEFISCH LANDS ANOTHER HIGH PROFILE CONSERVATIVE ENDORSEMENT

Asked by reporters on the eve of the primary for comments Trump’s derogatory attacks, Kleefisch responded: "No thoughts that I can share."

And she seemed to discount Trump’s endorsement of Michels as she emphasized in a Fox News interview on Monday that "the voters of Wisconsin are going to be the ones who determine the outcome of this race."

Former President Donald Trump and Wisconsin GOP gubernatorial candidate Tim Michels

Republican gubernatorial candidate Tim Michels speaks as former President Donald Trump listens at a rally in Waukesha, Wisconsin, on Friday, Aug. 5, 2022.  (AP Photo/Morry Gash, Fil)

Michels’ campaign attempted to frame Kleefisch as a never Trumper, writing in an email to supporters on primary eve that "if we don’t get Trump supporters to the polls to vote for Tim Michels on Tuesday, the Never Trumpers will win." And Michel’s campaign argued that if Kleefisch wins, "the media will falsely report Wisconsinites have rejected Trump’s endorsement."

Michels has also spent big bucks to run ads targeting Kleefisch, while the former lieutenant governor has criticized Michels - who owns a home in Connecticut - as a part-time Wisconsin resident.

The candidate Trump backed in last week’s GOP gubernatorial primary in Arizona, former TV news anchor Kari Lake, narrowly edged real estate developer and Arizona Board of Regents member Karrin Taylor Robson, who was supported by Pence.

But in May, conservative Republican Gov. Brian Kemp of Georgia, who was endorsed by Pence, trounced his Trump-backed challenger, former Sen. David Perdue, in the state’s GOP gubernatorial primary.

Besides Pence, two other potential 2024 GOP White House hopefuls, Sen. Ted Cruz of Texas and former South Carolina governor and former ambassador to the United Nations Nikki Haley, endorsed Kleefisch this summer. Haley campaigned with the former lieutenant governor and helped her fundraise.

Sen. Ron Johnson, R-Wisc., takes his seat for the Senate Foreign Relations Subcommittee on Europe and Regional Security Cooperation Subcommittee hearing in the Dirksen Senate Office Building on Wednesday, Feb. 16, 2022. (Bill Clark/CQ-Roll Call, Inc via Getty Images).

Sen. Ron Johnson takes his seat for a Senate Foreign Relations Subcommittee hearing in the Dirksen Senate Office Building on Feb. 16, 2022. (Bill Clark/CQ-Roll Call, Inc via Getty Images)

In Wisconsin’s high profile Senate race — one of a handful across the country that will likely determine if the Republicans win back the chamber’s majority in November —  GOP Sen. Ron Johnson is being heavily targeted by Democrats. Johnson faces a lone long-shot primary challenge on Tuesday from educator David Schroeder

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Democratic Lt. Gov. Mandela Barnes is his party’s all-but-certain Senate nominee on Tuesday, after his leading rivals dropped out of the race in recent weeks and endorsed him. Barnes is also backed by national progressive champions such as Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts and Rep. Alexandria Ocasio-Cortez of New York. Barnes is part of a primary field that also includes four lesser-known Democrats.

Democratic U.S. Senate candidate Mandela Barnes speaks

Wisconsin Lt. Gov. and Democratic U.S. Senate candidate Mandela Barnes speaks at a rally at John Marshall High School Friday in Milwaukee. (AP Photo/Morry Gash, File)

President Biden narrowly carried Wisconsin as he won the 2020 election, and on Friday at his rally, Trump blasted Republican state Assembly Speaker Robin Vos for not embracing his unproven claims that his 2020 loss to Biden was due to massive voter fraud. 

While Vos — who’s the state’s longest serving Assembly speaker — launched a controversial investigation into the 2020 election in Wisconsin and took a lead in passing a series of bills that tightened voting access in the state, he’s resisted Trump’s repeated calls to try and decertify the 2020 election results. 

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Trump, who days earlier backed Vos’ Republican challenger in the primary, urged those at the rally to "fire Robin Vos."

Minnesota

Democratic Gov. Tim Walz of Minnesota faces a long shot primary challenge as he seeks a second term. Three Republicans are running in their party’s primary, including doctor and former state Sen. Scott Jenson, who landed the state GOP’s endorsement. 

Rep. Ilhan Omar of Minnesota

Rep. Ilhan Omar, D-Minn., is seen in the U.S. Capitol's Rayburn Room on April 6, 2022. (Tom Williams/CQ-Roll Call, Inc via Getty Images)

There's a special election on Tuesday in the state's primarily rural 1st Congressional District, along the state's southern border with Iowa, to fill the seat left vacant after GOP Rep. Jim Hagedorn died of cancer in February. The winner will serve the remainder of Hagedorn's term through the end of the year.

But complicating matters is that this isn't the only election in the district. There's also the reguarly scheduled primary 

In the state’s Minneapolis-centric 5th Congressional District, progressive first-term Democratic Rep. Ilhan Omar, a member of the "Squad," is facing four primary challengers. One of them — former Minneapolis City Councilman Don Samuels — is endorsed by a handful of former Minnesota mayors and has spotlighted his law enforcement support while criticizing Omar for pushing to dismantle the city’s police department.

In Minnesota’s 5th Congressional District, in the Twin Cities southern suburbs, all eyes are on November’s general election, when Democratic incumbent Rep. Angie Craig and 2020 GOP nominee Tyler Kistner will face off in a rematch.

Connecticut

Three Republicans are running in Tuesday’s Senate GOP primary in Connecticut, with the winner facing off in November against Democratic Sen. Richard Blumenthal. They are former state House Minority Leader Themis Klarides, businesswoman Leora Levy and businessman Peter Lumai. 

It’s been 40 years since a Republican won a Senate election in the blue state of Connecticut.

Vermont

The Senate seat held for nearly a half century by retiring Democratic Sen. Patrick Leahy is up for grabs.

Longtime Rep. Peter Welch is considered the overwhelming front-runner over two other rivals in the Democratic primary. Former U.S. attorney Christine Nolan, Army veteran Gerald Malloy and investment banker Myers Mermel are seeking the Republican nomination.

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With Welch running for the Senate, there are competitive primaries in both parties for his open House seat.

Republican Gov. Phil Scott faces two primary challengers on Tuesday. Activist Brenda Seigel is unopposed for the Democratic gubernatorial nomination.

Fox News' Daniel Hillsdon and Grady Trimble contributed to this report