The Republican Senate primary in Pennsylvania remains wide open even after former President Donald Trump endorsed Mehmet Oz, with Oz and two other candidates forming a clear top tier, according to a new poll released Wednesday.

Lt. Gov. John Fetterman continued to enjoy clear advantages in the Democratic Senate race heading into the final three weeks before the May 17 primary, according to the Monmouth University survey.

Among Republicans, Oz and former hedge fund CEO David McCormick topped the field in a variety of measures, with conservative commentator Kathy Barnette apparently running close behind despite being vastly outspent on TV by her two wealthy rivals.

The poll, conducted April 20-25, was the first public survey done with any real time for voters to absorb Trump’s endorsement of the celebrity surgeon widely known as “Dr Oz.” It suggests that while Trump’s support may help Oz with almost a quarter of GOP voters, it isn’t enough to decisively shift the race.

And it’s the latest of several surveys to show Barnette emerging as the clear third-place candidate, positioning her to potentially benefit if Oz and McCormick continue tearing each other down — or if GOP voters sour on the two multimillionaires who only recently moved to Pennsylvania.

Most GOP respondents were already aware of Trump’s endorsements, and 22% said it made them view Oz more favorably. But months of attacks on Oz have taken their toll, with 37% of registered Republicans viewing him negatively and 42% saying they were not “too likely” or not at all likely to support him.

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The survey asked a variety of questions about the candidates and how voters view them, offering a nuanced picture of the race, with Oz leading by some measures, McCormick by others, and Barnette consistently in third — though with a margin of error of 4.9%, the poll suggests she could also be ahead or tied with those rivals on some measures. Less than 40% of GOP voters have settled on a single candidate they are “very likely” to support, leaving room for big shifts in the final days of the campaign.

“This is the kind of environment where a number of candidates could emerge as the nominee,” said Monmouth pollster Patrick Murray. “Oz has the highest name recognition but also the highest negatives. If McCormick and Oz beat each other up, though, Barnette could realistically end up on top.”

The Democratic field was more clear: Consistent with many other polls, Fetterman led by every measure Monmouth surveyed, with U.S. Rep. Conor Lamb second and State Rep. Malcolm Kenyatta third.

How voters view the GOP candidates

Oz (20%), McCormick (16%), and Barnette (12%) were the only Republican primary candidates who reached double digits on the question of who’s strongest on Republican voters’ top concerns: inflation and undocumented immigration.

A question about whom voters were “very likely” to support reflected the fluid race: 22% picked Oz, 19% McCormick, and 18% Barnette. Carla Sands, the former ambassador to Denmark, was at 9%, and Montgomery County real estate developer Jeff Bartos at 8%.

But with so many Republicans seeing Oz negatively, McCormick appeared to be running stronger with voters who are still somewhat undecided. When including those who were both “very” or “somewhat” likely to support a candidate, 61% said McCormick, 51% Oz, and 51% Barnette. Bartos was at 45% and Sands 42%.

Attorneys George Bochetto and Sean Gale trailed far behind.

McCormick had the strongest public image: 51% of Republicans saw him favorably, and just 15% viewed him unfavorably. For Oz, the numbers were 48% to 37%, and for Barnette 37% to 5%, though far fewer voters were familiar with her compared with the two GOP front-runners. (After tens of millions of dollars of TV advertising, Oz and McCormick are nearly universally known among GOP voters.)

McCormick and his allies have spent huge amounts on TV attacking Oz and his conservative credentials, and even after the Trump endorsement argued that the early negative impressions of the surgeon would weigh on him. The poll suggests that attacks on McCormick and his hedge fund’s investments in China have not resonated as widely.

» READ MORE: Is Mehmet Oz really a conservative? We looked at the Pa. Senate candidate’s record.

“If Dr. Oz thought Trump’s seal of approval was going to lock this nomination up for him, he was mistaken. It may help Oz on the margins, but it doesn’t completely erase his negatives,” Murray said.

Monmouth used questions about candidate image, likelihood of support, and other questions to provide a “fuller picture” of the race compared with traditional “horse race” polling, Murray wrote in an email. The decision comes after polls in some recent years, particularly when it comes to views of Trump, have missed the mood of the electorate.

A clearer Democratic field

On the Democratic side, Fetterman, who has led from the start, had by far the highest name recognition (81%) and a 68% favorable rating. Some 44% of registered Democrats were “very likely” to support him. He had stronger support from those who describe themselves as liberal than as moderate or conservative.

Lamb had a 51% favorability rating, but only 23% of Democratic respondents said they were “very likely” to support him in the primary. Kenyatta had a 32% favorable rating, and 14% said they were very likely to support him.

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Limiting the results to Democrats who show a clear preference for only one candidate, Fetterman led with 34%, compared with 12% for Lamb and 4% for Kenyatta.

When it comes to ideology, Democrats were divided: 46% (largely older voters) said they would like to see their moderate wing have more influence, while 42% (largely those under 50) wanted the progressive wing to gain power.

Some 23% of Pennsylvania Democratic respondents said they are very liberal, while 44% described themselves as moderates, the poll found.

Lamb is widely seen as the most moderate of the top candidates, with Kenyatta as a clear progressive. Fetterman has a progressive reputation but has tried to stake out some positions closer to the political center on issues such as fracking and Israel as the primary has unfolded.

Democrats cited a wide variety of issues as their top concerns, including inflation (28%), Russia’s attack on Ukraine (18%), health care (13%), the pandemic (12%), voting and democracy (11%), and environmental issues (11%).

The poll surveyed 407 registered Republicans and 406 registered Democrats and has a margin of error of plus or minus 4.9 percentage points.