Celebrity doctor Mehmet Oz, who is running as a Republican for Senate in Pennsylvania and is set to campaign Friday night with former President Donald Trump, is underwater with GOP voters, according to the latest Franklin & Marshall poll.

The survey, which was released roughly two weeks before voters go to the polls on May 17, found that all the candidates polled were in a virtual tie. But, it showed Dr. Oz has a negative favorability rating among Republican voters.

Of the Republican voters, 41 percent viewed him unfavorably, while only 29 percent viewed him favorably.

However, while Dr. Oz is underwater and endorsed by Trump, his primary opponent, David McCormick, shows a clear advantage with the faction of voters who have supported the former president.

Of those respondents, 29 percent said they were in favor of McCormick, while only 19 percent were in favor of Dr. Oz, and 18 percent said Kathy Barnette.

In the overall poll, there appeared to be a virtual tie as the three Republican candidates are all roughly within the margin of error.

Overall the Franklin & Marshall poll found a virtual tie between the top candidates with the 325 registered Republican Pennsylvania voter respondents and a margin of error of plus or minus 4.4 percent.

The poll found that 18 percent of Republican respondents said they would vote for Dr. Oz. In comparison, there were 16 percent who said they would vote for McCormick and 12 percent who said they would vote for Barnette.

The other candidates in the race were stuck in the single digits: Carla Sands showed five percent in the poll, Jeff Bartos showed two percent, Sean Gale showed one percent, and George Bochetto did not even get one percent in the survey. There were also five percent who said someone else, one percent said none, and 39 percent still did not know who to vote for.

Additionally, when the poll was taken, two-in-five respondents (39 percent) said they were not sure who they wanted to vote for in the Republican primary. But the poll showed that 57 percent of the respondents picked a candidate but said their minds could be changed.

The poll was conducted at the Center for Opinion Research at Franklin & Marshall with 325 registered Republican Pennsylvania voters. The interviews were conducted from April 20 to May 1 and showed a plus or minus 4.4 percent margin of error.

Jacob Bliss is a reporter for Breitbart News. Write to him at jbliss@breitbart.com or follow him on Twitter @JacobMBliss.