This month’s Republican primary election will determine which of three candidates will face independent Evan McMullin in the race for U.S. Senate in November.

But how do Becky Edwards, Ally Isom and Sen. Mike Lee stack up against McMullin if the general election were held today?

A new Deseret News/Hinckley Institute of Politics poll shows Lee and Edwards with slight edges over McMullin, though a large chunk of Utah voters — more than a third in an Edwards-McMullin matchup — are undecided. Utahns were more decisive if the election were to pit Lee against McMullin.

McMullin has a larger lead over Isom, but the survey found more than a third of voters don’t know who they would choose in that race. And though Isom trails McMullin by double digits in the poll, the bottom line is that the race for Senate in Utah could be one of the most competitive in decades with so many undecided voters up for grabs.

In an unprecedented move, the Utah Democratic Party voted to not advance a candidate in the Senate race and threw its support behind McMullin.

“This is turning out to be a highly competitive race and it’s because of how unique these candidates are. This will be the first time that, in effect, we’re going to see a general election with two Republican candidates,” said Jason Perry, director of the Hinckley Institute of Politics at the University of Utah. McMullin previously affiliated with the Republican Party.

The campaigns for all four candidates weighed in on the poll results, mostly taking shots at each other and especially at the incumbent Lee, who is seeking a third term.

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“People who vote in November for the United States Senate are essentially picking between two candidates that by all accounts would be called Republicans,” Perry said. “That is why we are seeing the race so close at this point.”

In the poll, 41% of Utahns would vote for Lee and 37% for McMullin in a general election. Another 19% don’t know who they would vote for, while 4% would choose someone else. Two third-party candidates have qualified for the November ballot.

Edwards led McMullin 29% to 28% in a head-to-head contest, according to the poll. But 37% of voters were undecided.

An Isom-McMullin matchup found McMullin getting 34% of the vote and Isom 23%, with 36% saying they don’t know.

Dan Jones & Associates conducted the poll of 810 registered voters in Utah from May 24 to June 4. It has a margin of error of plus or minus 3.46 percentage points.

The poll results show Lee has a modest lead right now over McMullin, but Edwards also appeals to voters when Lee is not in the equation, and Isom a little less so.

“What that tells me is Republican voters are paying close attention, not just to the party but to the individuals, particularly when the menu largely is Republicans,” Perry said. “There’s just no pure reliable Republican vote. Republicans are discerning. Whoever gets before them will have to win those votes.”

Lee is the favorite to take the June 28 GOP primary election. Mail-in ballots went out Tuesday. In an earlier Deseret News/Hinckley Institute poll, Lee had a substantial lead over Edwards and Isom, though less than half of those likely Republican primary voters would pick him.

The poll shows Lee has managed to maintain his solid Republican base, while McMullin picked up Democrats and voters who don’t belong to either party. The survey found 57% of Utahns who identified themselves as Republicans would vote for Lee, but 29% favor McMullin.

According to the poll, 64% of Democrats choose McMullin, though 29% said they don’t know. McMullin had the edge over Lee among unaffiliated voters 38% to 27%, with 28% undecided.

Utahns in the survey who identified themselves as “very” or “somewhat” conservative overwhelmingly chose Lee, while “very” or “somewhat” liberal voters went with McMullin. Moderate voters clearly favor McMullin, with the poll finding 54% would vote for him compared to 16% for Lee.

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In Utah, federal races are often determined in the Republican primary. Democrats have not put up competitive candidates, leading to lopsided outcomes in November. Utah simply has a lot more Republicans than Democrats, Perry said.

With no Democrat in the race and an independent who largely leans Republican, Utah voters are seeing a very different choice in the November election.

While Lee does well with Republican and conservative voters, only 39% of Utahns overall approve of his job performance in the Senate, while 41% disapprove, according to a Deseret News/Hinckley Institute poll 808 registered Utah voters conducted May 7-13. Those numbers could make him vulnerable in a general election.

McMullin campaign spokeswoman Kelsey Koenen Witt said the latest poll shows the Senate race is wide open and emerging as one of the most competitive in the country.

Utahns, she said, are tired of politics as usual and ready for an entirely new way in politics. Washington is broken and Lee is a big part of that, she said.

“He’s divisive and polarizing. Time and time again, he’s embarrassed our state and failed to deliver. Utahns can do better,” Koenen Witt said. “We’re working hard to bring voters together to find solutions and we’ll continue to build this coalition until Election Day and beyond.”

Matt Lusty, Lee campaign spokesman, said the senator’s internal polling numbers show him much further ahead of McMullin.

“As McMullin tries to appease the Democrats on Roe v. Wade, create new restrictions on the Second Amendment, and otherwise show support for Joe Biden’s agenda, Republicans and independents will see through his rhetoric of trying to be all things to all people,” he said.

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Lee’s GOP challengers are locked in on the primary election, according to their campaigns.

Edwards remains the only candidate with enough support to replace Lee, said Edwards campaign spokeswoman Chelsea Robarge Fife.

“Congress is broken and we need productive, proactive and inclusive leaders in the U.S. Senate,” she said, while inviting unaffiliated voters to register with the Republican party in order to vote in the primary election and encouraging Republicans to return their ballots as soon as possible.

Isom campaign spokeswoman Addie Thomas said the poll numbers are moving in the right direction as Utah voters get to know Isom as a “viable conservative alternative, in touch with everyday Utahns.”

Thomas said the campaign is focused on GOP primary voters and making sure they know their vote matters.

“It’s abundantly clear that a large number of Utahns are unsatisfied with the incumbent and open to a different kind of leader,” she said.