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 which also includes state lawmaker Timothy Ramthun. The GOP primary winner will face off in November with Democratic Gov. Tony Evers, who’s being heavily targeted by Republicans as he seeks a second term.

Michels — 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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"I am the one who is tested and proven and ready to go," Kleefisch said as she teamed up with Pence at a campaign stop in suburban Milwaukee on Wednesday. "I am 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."

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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."

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."

Evers faces no primary challengers on Tuesday. 

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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.

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.

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."

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. 

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.

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.

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.

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