The FBI is declining to investigate Supreme Court nominee Brett Kavanaugh's connection to a Democratic senator's mysterious claim that troubling 'information' had come to her – information reportedly concerning sexual misconduct when he was in high school.

Sen. Dianne Feinstein of California said Thursda in a statement that she had referred her information to federal investigators, just a week before the U.S. Senate is scheduled to begin a series of votes on his nomination.

Feinstein is a liberal California Democrat who has called on her colleagues to slow down the march toward confirming President Donald Trump's pick to succeed Justice Anthony Kennedy.

The Washington Post reported Thursday evening that the FBI handed the senator's materials over to the White House instead of opening a probe, and considered it an update to his background check file.

'Upon receipt of the information on the night of September 12, we included it as part of Judge Kavanaugh's background file, as per the standard process,' an FBI official told the Post.

The New York Times reported Thursday that Feinstein received a letter about the unspecified allegations against Kavanaugh 'this summer' – meaning she may have held onto it for dramatic effect at an inopportune moment for Republicans.

FBI request: Diane Feinstein has referred a letter she has received to the Justice Department. It reportedly concerns Brett Kavanuagh's high school behavior

The unnamed woman has reportedly retained Debra Katz, a prominent Washington D.C. attorney involved in the #MeToo movement

Debra Katz, a Washington, D.C. lawyer best known for representing women who make '#MeToo'-style accusations against powerful men, is reportedly representing the unnamed woman. Katz was seen leaving Capitol Hill on Wednesday night.

Feinstein is the ranking Democrat on the Judiciary Committee, which is considering Kavanaugh's nomination. Republicans are pushing to confirm him to the Supreme Court by Oct. 1, when its next term begins.

A tight-lipped Feinstein had released a cryptic statement saying that the woman who provided the information about Kavanaugh 'strongly requested confidentiality, declined to come forward or press the matter further, and I have honored that decision.'

Buzzfeed claimed Thursday that it believes it knows who Kavanaugh's potential accuser is, and has for at least a week, but hasn't been able to reach her to confirm it.

A White House spokeswoman complained about the timing of the vague and gauzy revelation.

'Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new "information" about him,' Kerri Kupec said.

Texas Republican Sen. John Cornyn mocked the idea of a legitimate bombshell that could sink Kavanaugh

'Let me get this strsight': Cornyn was in disbelief about what appeared to be the substance of Feinstein's letter

Cornyn also pointed out that the FBI had already cleared Kavanaugh and that committee Democrats had their report

Senate Minority Leader Chuck Schumer, she said, had 'promised to "oppose Judge Kavanaugh’s nomination with everything I have," and it appears he is delivering with this 11th hour attempt to delay his confirmation.'

Kupec added that the FBI had already 'thoroughly and repeatedly vetted Judge Kavanaugh, dating back to 1993, for some of the most highly sensitive roles.'

Judiciary Committee chairman Chuck Grassley, an Iowa Republican, told reporters outside a Senate hearing room that he hadn't seen the letter Feinstein is guarding.

'All I know is what I read, and I wouldn’t make any judgment of it until I get more information,' Grassley said.

Fellow committee Republican John Cornyn of Texas reacted with a digital eye-roll.

'Let me get this straight: this is statement about secret letter regarding a secret matter and an unidentified person. Right,' Cornyn tweeted.

In a second tweet, he added that 'the FBI already performed and has reported on a background investigation on the nominee and this has been made available to all Senators on the Judiciary Committee.'

Feinstein received her information in a roundabout fashion. The Intercept reported late Wednesday that the alleged incident was described to someone affiliated with Stanford University, who then wrote to Democratic Rep. Ana Eshoo, who represents the area.

Eshoo passed the letter to Feinstein, but neither lawmaker will describe what's in it. Eshoo's office says it's considered part of an active and confidential constituent-service case.

Feinstein is closely guarding it, refusing to share it even with her fellow Judiciary Committee Democrats.

She complained Thursday during a committee meeting that Republicans were rushing engaged in a 'rush to judgement' as they moved to close the file on Kavanaugh before its full contents could be examined.

Republicans have already provided Democrats with an avalanche of documents, including tens of thousands from his time serving as staff secretary in the George W. Bush White House.

'What in Judge Kavanaugh's records are Republicans hiding?' Feinstein exclaimed.