Senate Democrats are raising new concerns about the thoroughness of the FBI’s background investigation of Supreme Court Justice Brett Kavanaugh after the FBI revealed that it had received thousands of tips and had provided “all relevant” ones to the White House counsel’s office.

Responding to Democrats’ long-standing questions, the FBI revealed in a late December letter that it had received over 4,500 tips during its investigation of the past of the nominee following Donald Trump’s 2018 nomination. Jill Tyson, an assistant FBI director, wrote on behalf of Director Christopher Wray that this was the first time the FBI had established a tip line for nominees undergoing Senate confirmation.

In a Wednesday letter, a group of Democratic senators stated that Wray’s response “raises substantial additional questions.” They asked him to clarify, among other things: how many tips were considered relevant by the FBI, what criteria agents used to determine that, and what policies and procedures were used for vetting tips. They also requested more information on the tip line, including its staffing and preservation.

The senators replied, “Your letter confirms the FBI’s tip-line was a departure form past practice and that FBI was politically constrained under the Trump White House.”

Kavanaugh was confirmed to the Supreme Court in October 2018 after a rancorous process in which claims emerged that he had sexually assaulted women three decades ago. The allegations were denied by Kavanaugh who strongly denied them.

Wray stated that the FBI conducted an initial background investigation into Kavanaugh. This included interviews with 49 people over five days. After new information was discovered about Christine Blasey Ford (a woman who claimed Kavanaugh assaulted her as a teenager), the bureau did a supplemental background investigation. Wray stated that the FBI interviewed 10 people in six days as part of this process.

He stressed that the inquiry was not comprehensive and did not include the “authorities policies and procedures” required for an FBI criminal investigation.

Ford lawyers stated in a statement that the FBI letter had established that the investigation was a “sham” and a “major institutional failure”. They also criticized the bureau for failing to interview Ford or for acting on the many tips it received regarding Kavanaugh.

“Instead, it gave the information to the White House, which allowed those who supported Kavanaugh falsely claim that there was no wrongdoing,” stated Lisa Banks and Debra Katz.