President Biden's decision to go back on his word and pardon his son will be a permanent stain on his legacy, a presidential historian said Thursday.

Douglas Brinkley, a professor at Rice University argued to USA Today that there is "nothing positive" about Biden's decision. The pardon has already drawn criticism from Republicans and even Biden's allies in Congress.

"The problem that President Biden has legacy-wise is he said he wouldn't pardon his son," Brinkley said. "He gave his word, crossed his heart, and then, alas, he ended up doing it. It will strike some people as unfair and other people will say it’s a father doing what he had to."

He added that the pardon will only serve to be a "dark mark" on Biden's term moving forward.

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Brinkley also noted the trouble Hunter has caused for his father's presidency since gaining office. Investigations into the first son have resounded through Congress and the media, providing a counterpoint to then-ongoing criminal investigations into President-elect Trump.

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"Hunter Biden's been an albatross around his father's neck for the entire presidency," Brinkley said.

Brinkley goes on to argue that Trump's victory in November may have been the deciding factor, with Biden fearing that the incoming administration would target his son with more investigations.

Nevertheless, the move won him no allies. California Gov. Gavin Newsom, typically a staunch ally of the president, said he was "disappointed" in the decision and that he "cannot support it."

Rep. Pete Aguilar, D-Calif., who chairs the Congressional Democratic Caucus, also said he was "disappointed" in the decision Wednesday. He went on to note that Biden had gone back on his word.

Biden had vowed multiple times that he would not intervene in his son's case, first in June when his son was convicted on three felony firearm charges, and then in September after Hunter pleaded guilty to federal charges of tax evasion.

"I am not going to do anything," Biden said this summer. "I will abide by the jury’s decision."