A former top FBI official said Thursday that President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE’s possible commutation of former Illinois Gov. Rod Blagojevich's (D) prison sentence is an act of retribution for special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s probe.

Robert Grant, a longtime friend and colleague of Mueller who led the FBI’s Chicago office during its investigation into Blagojevich, told Politico that Trump was trying to undermine the bureau’s work in response to Mueller’s investigation into Russian meddling in the 2016 presidential election.

“It’s so disheartening to think that the president of the United States would overturn the evidence heard by a judge and jury, all out of an animus toward Bob Mueller, James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE and [former U.S. Attorney] Pat Fitzgerald,” Grant said.

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Mueller headed the FBI during the investigation into Blagojevich. Former FBI director James Comey was the bureau’s attorney general and Pat Fitzgerald was the U.S. attorney in Chicago.

“Blagojevich got caught by wiretaps and microphones and he was engaging in a practice that we believed he was taking part in for quite awhile,” he continued. “I don’t think anybody who listened to those tapes would think anything but it was an incredibly corrupt governor who was dealing with corrupt associates.”

Grant, who has since retired from the agency, added that Trump’s comments on Blagojevich and his pardon of Lewis “Scooter” Libby earlier this year are all part of an effort to undermine Mueller’s probe.

“So if Trump gets himself into an obstruction of justice case or lies, then that’s OK. But that’s not the case for the poor kid on the South Side,” Grant told the outlet. “I think [Trump] tries to hurt anybody he doesn’t like. He will use his office because he can. Not to use it judiciously, but out of spite and animus.”

“When the framers of the Constitution framed that power, I don’t think they envisioned this,” he added.

Trump told reporters earlier Thursday that he was considering commuting Blagojevich’s sentence and pardoning TV star Martha Stewart, both of whom have ties to Trump's reality TV show, "The Apprentice."

The president called Blagojevich’s 14-year sentence "really unfair." The former governor was sentenced in 2011 on corruption charges, including trying to sell former President Obama’s old Senate seat.

Trump also pardoned conservative commentator Dinesh D'Souza on Thursday, who pleaded guilty in 2014 to making illegal campaign contributions.

Trump has repeatedly attacked Mueller’s probe as a “witch hunt” and has claimed that the investigation is biased against him.