In the fight to control the United States Senate, Republicans are facing an unexpected problem in the battleground state of Arizona — the Libertarians.

The first poll released after Thursday’s Arizona Senate debate shows the Trump-backed Republican, Blake Masters, losing ground to the incumbent Democrat, Mark Kelly, with a surge by the Libertarian nominee, Marc Victor.

The Arizona-based OH Predictive Insights poll finds Mr. Victor with 15 percent support, a 9-point bump from its last poll in September. This surge in support more than makes up the difference between Mr. Masters’s 33 percent and Mr. Kelly’s 46 percent.

Mr. Victor tells the Sun this is “evidence” that Arizona voters want change and are attracted to his “live and let live” libertarian message. He rejects the notion he is a “spoiler” candidate who will tip the scale in Mr. Kelly’s favor.

“I am not running to be a spoiler,” Mr. Victor tells the Sun. “No Libertarian has ever won a major political election — that’s not evidence it can’t happen.”

Republicans should be worried. While this recent poll is an outlier, Mr. Masters is consistently trailing Mr. Kelly in polls, and the libertarian vote could decide the election. In 2020, President Trump lost to Vice President Biden in Arizona by 0.3 percent, while the Libertarian candidate, Jo Jorgensen, got 1.5 percent of the vote. 

After a recent candidate debate, Mr. Victor addressed calls for him to step down in a video he released on social media. “If either one of those candidates, either Senator Kelly or Blake Masters, wants to talk to me about stepping down and endorsing them, I am absolutely willing to have that conversation and I will bring an open mind to the conversation,” he says to the camera. His one condition: The meeting must be videotaped, unscripted, and released to the public.

“If I’m convinced that it’s in the interest of freedom and peace and civility for me to step down and endorse one of them, that’s exactly what I’ll do,” he tells the Sun.

So far, he’s gotten no response from either campaign. Mr. Kelly’s campaign, though, is no doubt happy to see Mr. Victor’s star rising. 

During the debate, Mr. Victor criticized Mr. Masters for avoiding the question on whether he scrubbed his campaign website to soften his opposition to legalized abortion.

“This evasiveness from Blake Masters is exactly why you should have a principle and stick with it,” Mr. Victor said. He then went on to describe his position on abortion: Leave it to localities — cities and counties — to decide what laws they want for their communities.

On inflation, Mr. Victor took a standard libertarian position, attacking reckless spending — a dig aimed mainly at Mr. Kelly and the Democrats. “We need to get back to sound money again so the government can’t continue to have no limit on their credit card,” he said.  

Mr. Victor says he is trying to focus on “what I call the reasonable people, not the radicals on the left, not the radicals on the right.” He did, though, get negative press for proposing at the debate a referendum on the age of consent, which angered many in the Libertarian Party.

In an unexpected twist, the Libertarian Party’s presumptive nominee for president in 2024, Dave Smith, a comic and podcaster, endorsed Mr. Masters on Twitter. 

“This guy is a clown who has absolutely nothing to do with us. He went outside the party and got signatures to be on the ballot,” Mr. Smith tweeted about Mr. Victor. “I support Masters.”

This sparked a fierce debate on Libertarian Twitter. “The national party has not endorsed him,” Libertarian National Committee chairwoman, Angela McArdle, tells the Sun. She calls Mr. Victor’s comment on age of consent “tone deaf,” and she has other reservations, but she adds, “Otherwise, I think he sounds like he’s a pretty good candidate.”

Mr. Victor says he doesn’t even know if he is a member of the national Libertarian Party. “I am absolutely a lone wolf,” he says, adding that his “preference would have been to run as an independent,” but the ballot requirements were onerous.

Mr. Masters, meanwhile, is positioning himself as the libertarian choice. His website mixes standard MAGA policies with a section on “Make America Free Again,” which lists his positions in favor of Bitcoin and protecting the Second Amendment and free speech, especially from big tech censorship.

The Libertarian challenge expressed in one poll is not necessarily indicative of how Arizona voters will act in the ballot box come Election Day. This is a hotly contested race that could determine the Senate balance. Even Mr. Victor recognizes the “spoiler” label is hard to overcome.

“The time is right. People are frustrated,” Mr. Victor says. “I think if people actually think I have a chance of winning that I will win.”