Donald Trump's embattled Supreme Court nominee Brett Kavanaugh was hit by a second accusation of sexual misconduct on Sunday, leaving Republicans scrambling to save a confirmation that until recently had seemed all but certain.

The latest claims of impropriety during Kavanaugh's youth came as he was already facing a dramatic hearing where his testimony was to be weighed against that of a university professor who has separately accused him of assault.

Senate Democrats are now investigating a bombshell claim by Deborah Ramirez, 53, who says Kavanaugh exposed himself to her during a 1980s college party at Yale University, thrust his genitals in her face and caused her to touch them without her consent, according to The New Yorker.

Kavanaugh denied the story, calling it "a smear, plain and simple".

"The people who knew me then know that this did not happen, and have said so," the conservative judge said in a statement.

Like Christine Blasey Ford, the professor accusing him of assaulting her when they were teenagers, Ramirez wants the FBI to investigate the incident and Democratic legislators are backing their demands.

Al Jazeera's John Hendren, reporting from Washington DC, said the latest accusation has put the whole process in turmoil.

"If every Democrat voted against Kavanaugh they will only need two Republicans to vote with them and this might be enough to make up that margin. So, the committee has a lot to think about in the coming days." (Aljazeera)