SALT LAKE CITY (AP) — Four Utah Republicans battling to win the seat of retiring U.S. Sen. Mitt Romney face off Monday evening in a debate that could begin to gauge the type of conservative who most appeals to voters statewide.

The marquee event in a marathon week of primary debates will test former President Donald Trump’s broad influence in Utah, one of the few red states that has been hesitant to embrace him. Trump’s day-of endorsement of a little-known mayor helped the local official to win the party nomination over nearly a dozen contenders at the April convention.

Romney has long been the face of the party’s more moderate wing, and his retirement from the Senate opens a door for candidates farther to the right. Observers are closely watching whether voters select a successor whose politics align more with Romney’s or with Utah’s other U.S. senator, Trump supporter Mike Lee.

While moderate U.S. Rep. John Curtis is considered the favorite going into the June 25 primary, convention victor Trent Staggs and former Utah House Speaker Brad Wilson, another Trump supporter, could push Utah politics further right in the post-Romney era.

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Curtis, Wilson and businessman Jason Walton had already guaranteed their spots on the primary ballot through signature gathering before the convention and will be joined on the debate stage by Staggs.

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Staggs, 49, built his base by calling state GOP delegates and courting the endorsements of Trump and many of his allies nationwide. The mayor of Riverton, a suburb south of Salt Lake City, was the first candidate to enter the Senate race, even before Romney announced he was not seeking reelection. Staggs’ convention victory may not translate to success at the ballot box, as Republican Party nominations historically have had little bearing on the decisions of Utah voters.

Curtis has been compared to Romney for pushing back against hardliners in his party, particularly on climate change, but has distanced himself from the retiring senator while campaigning for his seat. The 63-year-old Republican congressman and former mayor of Provo began his political career as a county-level Democratic Party official. He’s now the longest-serving member of Utah’s U.S. House delegation and has pitched himself as the only candidate who already understands the inner workings of Capitol Hill.

Wilson, who is endorsed by Gov. Spencer Cox and other top state officials, insists he’s already had the greatest impact on Utah residents as a state legislative leader. As House speaker, he oversaw years of tax cuts and budget negotiations that he says will help him fight federal overspending. Wilson, 55, has touted plans to soften federal regulations that he says stand in the way of local officials detaining immigrants who are living in the U.S. illegally.

The winner of the Republican Senate primary will face Democrat Caroline Gleich, a mountaineer and environmental activist, in November. Utah has not elected a Democrat to the U.S. Senate since 1970.

The Republican Senate debate is one of three scheduled for Monday in Utah. Challengers for two of the state’s four congressional seats are set to debate earlier in the day. Candidates for governor, attorney general and Curtis’ open U.S. House seat will face off Tuesday and Wednesday.