Democratic Sen. Sheldon Whitehouse on Monday told Attorney General Merrick Garland that he should look into the background investigation the FBI did of Justice Brett Kavanaugh during his confirmation process, alleging that the probe may have been "fake." 

Whitehouse, D-R.I., made the allegation in a letter that also addressed other issues like fossil fuel, political spending and the politicization of the Office of Legal Counsel.

But he also asked the newly minted attorney general to turn his attention to the 2018 allegations of sexual assault against Kavanaugh, which were never substantiated but turned his confirmation process upside down.

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"The second matter of concern is what appears to have been a politically-constrained and perhaps fake FBI investigation into alleged misconduct by now-Supreme Court Justice Brett Kavanaugh, rather than what Director Wray promised: a background investigation 'consistent with [the FBI’s] long-standing policies, practices, and procedures,'" Whitehouse wrote. 

Whitehouse's decision to resurface the allegations against Kavanaugh comes as a top Democratic governor, New York's Andrew Cuomo, is battling misconduct allegations.

Brett Kavanaugh testifies before the Senate Judiciary Committee.

He added that "If standard procedures were violated, and the Bureau conducted a fake investigation rather than a sincere, thorough and professional one, that in my view merits congressional oversight to understand how, why, and at whose behest and with whose knowledge or connivance, this was done."

"If ... the 'investigation' was conducted with drawbridges up and a fake 'tip line' and that was somehow 'by the book,' as Director Wray claimed, that would raise serious questions about the 'book' itself," Whitehouse said. 

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An official familiar with the Kavanaugh pushed back on Whitehouse's assertions, saying that the investigation "was not 'fake' as Senator Whitehouse suggests." The official also noted that the White House Counsel's office was the agency that set the parameters for the background check, not the FBI, and said that the FBI followed standard procedure during the Kavanaugh investigation, including setting up a real tip line. 

Whitehouse has a history of eccentric claims and actions consistent with his accusation that the FBI conducted a "fake" background check. During the confirmation hearing of Justice Amy Coney Barrett, he didn't question the nominee but instead explained, using charts, alleging that "outside forces are here pulling strings." He was speaking about "dark money" advocacy groups, which is a name for political groups on both sides of the aisle that are not required to disclose their donors. Whitehouse, however, only spoke about right-leaning groups in that category and not the litany of left-leaning groups that do similar work. 

Whitehouse also appeared to impugn the integrity of Republican-appointed Supreme Court justices in a 2019 Supreme Court brief before warning: "The Supreme Court is not well. And the people know it. Perhaps the Court can heal itself before the public demands it be 'restructured in order to reduce the influence of politics.'"

Kavanaugh was alleged by a woman named Christene Blasey Ford to have assaulted her when Kavanaugh was in high school. Her allegation -- along with a string of others that were far less credible -- prompted a second hearing on Kavanaugh's nomination and a subsequent supplemental FBI investigation into the then-nominee. 

Sen. Sheldon Whitehouse, D-R.I., speaks during the confirmation hearing for Supreme Court nominee Amy Coney Barrett before the Senate Judiciary Committee, Tuesday, Oct. 13, 2020, on Capitol Hill in Washington. (AP Photo/Patrick Semansky)

But Democrats were never satisfied with the scope of the supplemental investigation and have continued to push FBI Director Christopher Wray and the DOJ on the issue. With Biden's appointee Garland at the helm of the DOJ, Whitehouse now hopes to get more information. 

"In July 2019, Director Wray appeared at an oversight hearing before the Senate Judiciary Committee, where he assured senators he was 'committed to making sure the FBI does all of its work by the book, utterly without partisan interference,'" Whitehouse wrote. "But Director Wray has refused to answer Congressional inquiries about whether that was actually the case. Senators’ Questions for the Record from that July 2019 oversight hearing remain unanswered today, as does Senator Coons’ and my letter of August 1, 2019."

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Kavanaugh firmly denied the allegations against him, calling Democrats' efforts to stop his confirmation a "circus."

"You sowed the wind for decades to come," Kavanaugh said of Democrats' behavior and promotion of the allegations against him. "I fear that the whole country will reap the whirlwinds."

He continued: "This whole two-week effort has been a calculated and orchestrated political hit, fueled with apparent pent-up anger about President Trump and the 2016 election, fear that has been unfairly stoked about my judicial record, revenge on behalf of the Clintons and millions of dollars in money from outside left-wing opposition groups."

Fox News' David Spunt contributed to this report.