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Reached late Friday, the FBI referred questions to the White House. The White House declined to answer specific inquiries.
Such a probe is not unprecedented.
The FBI reopened its background investigation of then-Supreme Court nominee Clarence Thomas in 1991 after the allegations from Anita Hill came to light.
The investigation lasted three days. Former Vice President Joe Biden, who presided over the hearings, said the committee could not rely on the FBI report because it was "inconclusive" — a point that several Republican senators re-emphasized on Thursday.
Senate Judiciary Chairman Chuck Grassley echoed a quote from Biden after several Democratic senators asked Kavanaugh to commit to an FBI probe.
"The next person who refers to an FBI report as being worth anything obviously doesn’t understand anything. The FBI explicitly does not in this or any other case reach a conclusion. Period," Grassley said.
After Trump called for the FBI probe of Kavanaugh, Biden released a strongly-worded statement Friday defending his handling of the Hill hearings and praising the decision to reopen the FBI background investigation.
"Despite every effort to distort my words and record, I insisted on and got an FBI investigation 27 years ago," Biden said. "It was the right thing to do then and it is the right thing to do now."
In Kavanaugh’s case, the agents will likely have particular interest in speaking with Mark Judge.
Ford said Judge, a close high school friend of Kavanaugh's, was in the room when he pinned her to a bed, tried to pull off her clothes and clasped his hand over her mouth to stifle her screams.
Judge had sent letters to the committee saying he did not recall any encounter between Kavanaugh and Ford.
But late Friday, Judge said in a letter to the committee that he was willing to cooperate with the FBI probe.
An attorney for PJ Smyth, another person who Ford said was in the house when she was attacked, said his client "is happy to cooperate fully with this FBI investigation."
As for the the time frame, experts say the work can be done in a matter of days in most circumstances.
Ron Hosko, a former FBI assistant director, said background investigations done by the bureau typically have short turnaround times because the requesting agency needs the information quickly in order to make a decision on the nominee.
The FBI cannot force someone to talk to them as part of the process.
"Based on what we publicly know as far as the universe of people, I don't see any reason why the FBI could not complete an investigation within one week," said Mark Zaid, a Washington lawyer and expert in security clearance and background investigations.
"Remember, they're not reaching a decision or recommendation. They are just compiling the investigation and reporting on it."