About half of U.S. voters believe that special counsel Robert Mueller is being fair in his probe into possible collusion between the Trump campaign and Russia, according to a new poll.

A Quinnipiac University poll released Tuesday found that 51 percent of respondents surveyed thought the Mueller is running a fair investigation.

The respondents are split as to whether President Trump is guilty of wrongdoing in the probe: 42 percent said he is guilty, while 43 percent said he is not.

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Trump has repeatedly attacked Mueller’s probe, calling it “rigged” and a “witch hunt.”

The president went after the investigation in a series of tweets early Tuesday, seizing on the firing of FBI agent Peter Strzok, who was removed from the Mueller investigation after he was found to have exchanged anti-Trump texts with then-FBI lawyer Lisa Page.

Tom Fitton of Judicial Watch: “The Strzok firing is as much about the Mueller operation as anything else. There would be no Mueller Special Councel to investigate so called collusion but for the machinations of Strzok & his colleagues at the top levels of the FBI. We know this…

— Donald J. Trump (@realDonaldTrump) August 14, 2018

….guy was corrupt and had anti-Trump animus. Strzok and others at the FBI should be criminally investigated for the way the conducted this investigation. Instead, Mueller is pretending nothing went wrong. He used Strzok, he used the Clinton DNC Dossier…the whole thing….

— Donald J. Trump (@realDonaldTrump) August 14, 2018

….should be shut down. The Strzok firing shows that the fundamental underpinnings of the investigation were corrupt. It should be shut down by the courts or by honest prosecutors.” Thank you Judicial Watch, I couldn’t have said it better myself!

— Donald J. Trump (@realDonaldTrump) August 14, 2018

Strzok was fired Friday, but his dismissal was first reported on Monday. His attorney alleged that the firing “is not only a departure from typical bureau practice, but also contradicts Director [Christopher] Wray’s testimony to Congress and his assurances that the FBI intended to follow its regular process in this and all personnel matters.”

The FBI said that “Strzok was subject to the standard FBI review and disciplinary process.”

Quinnipiac University surveyed 1,175 American voters through landlines and cell phones from Aug. 9-13. The poll has a margin of error of 3.4 percentage points.