WASHINGTON — Sudden new revelations in Supreme Court confirmation fights are not new. Anita Hill’s accusations of sexual harassment against Clarence Thomas surfaced after his initial hearings had concluded. Justice Neil M. Gorsuch, President Trump’s first nominee to the court, faced claims that he had plagiarized parts of his book just as his nomination headed toward a Senate floor vote.

Now the bitter and extremely contentious Senate fight over the Supreme Court nomination of Judge Brett M. Kavanaugh has taken its own post-hearing turn with the disclosure that a top Democrat had for weeks possessed a letter accusing the nominee of sexual misconduct while he was in high school. The development, coming a week before the Judiciary Committee is scheduled to vote on his nomination, did not yet appear to be impeding Judge Kavanaugh’s steady progress toward assuming a seat on the court this fall.

Even after new details about the accusation became public on Friday, the office of Senator Charles E. Grassley, the Iowa Republican who is the chairman of the panel, said the committee vote would proceed as scheduled. In a statement, the committee noted that no similar allegations had ever arisen during six F.B.I. background investigations from 1993 to 2018, and that the “anonymous allegations are reportedly from Judge Kavanaugh’s high school time roughly 35 years ago.”

Senator Dianne Feinstein of California, the senior Democrat on the Judiciary Committee, first confirmed the existence of the letter on Thursday, just hours after the Republican-controlled panel had shut down multiple attempts by Democrats to extend the review of Judge Kavanaugh over separate issues related to his testimony and his time in the White House as an aide to President George W. Bush.