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Just weeks before a high-stakes confirmation vote, Sen. Dianne Feinstein has referred a letter that reportedly contains a Bay Area woman’s highly sensitive allegation about Trump Supreme Court nominee Brett Kavanaugh to the FBI.

The revelation roiled Capitol Hill on Thursday, after Feinstein issued a brief, cryptic statement about turning over information on the judge from a person who “strongly requested confidentiality.” With the partisan fight over Kavanaugh growing ever more heated, the White House swiftly labelled the move an 11th-hour desperation ploy by bitter Democrats.

Feinstein’s statement came after back-room discussion of a secret letter about Kavanaugh began to circulate more widely in recent days. It’s unclear who wrote the letter, but congressional sources said the document was originally sent to Rep. Anna Eshoo, a Palo Alto Democrat, before it was passed on to Feinstein, the ranking Democrat on the Senate Judiciary Committee.

The New York Times and Washington Post both reported that sources familiar with the letter say it included an allegation of sexual misconduct involving Kavanaugh when he was in high school. Sources told the Bay Area News Group the woman who raised the allegation is a Bay Area resident and a constituent of Eshoo.

“I have received information from an individual concerning the nomination of Brett Kavanaugh to the Supreme Court,” Feinstein said in the statement. “That individual strongly requested confidentiality, declined to come forward or press the matter further, and I have honored that decision. I have, however, referred the matter to federal investigative authorities.”

An FBI statement said the information was received Wednesday evening and then included in Kavanaugh’s background file, which is maintained as part of his nomination, the Associated Press reported. The agency said that’s standard process. The statement gave no indication that the information in the letter was being investigated. The New York Times and Washington Post, quoting unnamed officials, said the FBI has not opened a criminal investigation regarding the matter.

The Intercept first reported the existence of the letter Wednesday afternoon. Other Democrats on the committee had requested to see the letter and Feinstein did not provide it, the news website reported.

Kavanaugh, a federal appeals court judge, is seen as likely to be confirmed by the Senate to the Supreme Court, potentially shifting the Court to the right for a generation. However, the Senate Judiciary Committee on Thursday stalled a confirmation vote until Sept. 20. A full Senate vote is expected at the end of the month.

Kavanaugh grew up in the Washington, D.C., area and attended Georgetown Prep, a Jesuit boys high school in Bethesda, Maryland. It isn’t clear how the woman behind the letter is connected to him or why she approached Eshoo.

Emma Crisci, an Eshoo spokeswoman, said she could not comment because of her office’s confidentiality policy for constituent casework.

Other Bay Area Democrats were also silent about Thursday’s developments, but Republicans were furious by even the hint of such a highly sensitive accusation more than two months after Trump nominated a judge portrayed as a strong family man.

“Throughout his confirmation process, Judge Kavanaugh has had 65 meetings with senators — including with Senator Feinstein — sat through over 30 hours of testimony, addressed over 2,000 questions in a public setting and additional questions in a confidential session. Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new ‘information’ about him,” White House spokeswoman Kerri Kupec said Thursday.

She said the FBI has “thoroughly and repeatedly vetted” Kavanaugh dating back to 1993 for “some of the most highly sensitive roles.”

“This letter is incredibly unfair to Judge Kavanaugh and only shows how low and desperate Democrats have become,” Judiciary Committee member Sen. Mike Lee, R-Utah, said.

“It’s very disconcerting for this to surface now when the mysterious letter has reportedly been in Senator Feinstein’s possession for over a month,” added Matt Whitlock, a spokesman for Sen. Orrin Hatch, another Republican on the committee.

The New York Times reported that the letter was dated July 30, but it is unclear when it made its way from Eshoo’s office to Feinstein.

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Ted Cruz blocks Senate resolution honoring Ruth Bader Ginsburg Feinstein’s staff declined to give more details about when she received the letter or her decision-making process around releasing it. But the senator likely faced a difficult choice if she received a report of alleged misconduct but the individual involved did not want to go public, said Melissa Michelson, a political science professor at Menlo College.

Feinstein, who became one of the two first women ever appointed to the Judiciary Committee in January 1993, was elected just a year after the contentious Supreme Court hearing of Clarence Thomas, when Anita Hill, a former Thomas employee, accused him of sexual harassment. Those allegations led to weeks of political conflict and intense scrutiny on Hill’s personal life.

“At the time, there were no women on the Judiciary Committee,” Michelson said. “This certainly appears to be a very different case, but when somebody is brought forth before this committee and there might be a situation like that, Feinstein is probably thinking, ‘I need to stand up for that woman.’ “