A new letter from the FBI suggests it's unclear whether the agency followed up on the "most compelling" of the 4,500 tips it received in its investigation into Supreme Court Justice Brett Kavanaugh almost three years ago, The New York Times reported Thursday. The agency reportedly handed the most "relevant" tips to Trump administration lawyers, "whose handling of them remains unclear."

The letter, sent June 30, comes as a response to a 2019 inquiry from Sens. Sheldon Whitehouse (D-R.I.) and Chris Coons (D-Del.) asking how exactly the FBI's review of Kavanaugh's background and misconduct allegations was handled, the Times writes. In its reply, the FBI claims that because it was conducting a background check rather than a criminal investigation, "the authorities, policies, and procedures used to investigate criminal matters did not apply," per the Times. Kavanaugh was being investigated following allegations of sexual assault levied by Christine Blasey Ford, which he has denied.

"The admissions in your letter corroborate and explain numerous credible accounts by individuals and firms that they had contacted the FBI with information 'highly relevant to ... allegations' of sexual misconduct by Justice Kavanaugh, only to be ignored," Whitehouse and Coons wrote in a Thursday response, signed by five other senators. "Your letter confirms that the FBI's tip line was a departure from past practice and that the FBI was politically constrained by the Trump White House," they added earlier, on Wednesday. 

The lawmakers called on the FBI to answer a "range of outstanding questions" regarding the tip line and "the relevant information it yielded."

The Trump administration reportedly "carefully controlled" the inquiry into Kavanaugh's confirmation, writes the Times. Although it later allowed the FBI to "conduct a more open investigation," the White House initially tried to limit the number of people the agency could interview. Read more at The New York Times.