According to ABC television, "corroborating witnesses" have been found who caught the President and the then 21-year-old trainee, Monica Lewinsky, "in an intimate act" in the White House.
But in tape-recordings made by a confidante, Ms Lewinsky maintains that no one ever caught her with President Clinton or knew of presents she says he gave her. The tapes - obtained by Newsweek magazine - have Ms Lewinsky admitting to oral sex and late-night telephone sex sessions with the President and agonising about her decision to deny the affair.
The most damaging aspect of the scandal so far has been the accusation that Mr Clinton tried to persuade Ms Lewinsky to deny any relationship. That, rather than the alleged affair, was seen as the one issue that, could bring him down. The new evidence, however, believed to be in the hands of the independent prosecutor, Kenneth Starr, would throw doubt on the President's veracity.
Ms Lewinsky's lawyer, William Ginsburg, did the rounds of the American television talk shows yesterday and said that she would "absolutely, unequivocally" tell the full story about her relationship with Mr Clinton in return for immunity.
He said Ms Lewinsky stood by her affidavit in which she denied the relationship. But sources have indicated that she would be willing to change her story in exchange for immunity.
The television networks also showed clips of Ms Lewinsky being greeted by Mr Clinton at a rally shortly after his re-election in 1996. Ms Lewinsky appears adoring, but - as commentators stressed - Mr Clinton's feelings were impossible to judge as his cordiality is an integral part of his political persona.
Detectives from the FBI searched Ms Lewinsky's flat on Saturday, taking clothing, jewellery and her computer. Her lawyer said they were looking for proof of her relationship with Mr Clinton, including a dress that might provide DNA evidence of a sexual encounter.
Mr Clinton maintained his silence yesterday, but the White House went into more combative mode. Ann Lewis, communications director, was one of several senior officials to appear on the talk shows to defend the President, forcefully repeating his initial denials.
Not all Mr Clinton's allies were so supportive, however. His former chief of staff, Leon Panetta, told the San Jose Mercury newspaper that if the accusations had any truth in them, it would be better for the Democrats "if Al Gore became President and you have a new message, a new individual up there". Another erstwhile ally, George Stephanopoulos, Mr Clinton's former spokesman, also betrayed doubts. He said: "If he is telling the truth, he can survive. If he isn't, he can't."
A dozen or so White House advisers, contacted by CNN, were reported as saying that "the R-word" - resignation - was a real possibility, though a White House spokesman denied it had been mentioned. He also denied reports that the annual State of the Union address, scheduled for tomorrow, could be postponed.Reuse content