Republican presidential nominee Donald Trump has accused rival Hillary Clinton of being “pumped up” during their last debate, saying they should both be tested for drugs before the next one.
He also suggested the presidential race was looking like a “rigged election”.
The comments came in the wake of the publication of a recording in which he made obscene remarks, which sparked a string of sexual assault claims.
Polls suggest Mr Trump is losing ground in some of the key battleground states.
Speaking at a rally in New Hampshire, Mr Trump said Mrs Clinton had been “all pumped up” at the beginning of the last debate but could “barely reach her car” at the end.
“We should take a drugs test,” he said.
He did not provide any evidence to back up his claim.
Republican House of Representatives Speaker Paul Ryan said he was “fully confident” that the November election would be carried out “with integrity”, according to his spokeswoman AshLee Strong.
Mr Ryan, the most senior elected US Republican official, has said he will not defend Donald Trump in the wake of the recording of the nominee’s obscene comments.
However, Mr Ryan has stopped short of ending his endorsement of the Republican candidate.
The latest person to come forward is 63-year-old Cathy Heller, who told the Guardian newspaper that Mr Trump grabbed her and “went for the lips” during their first and only meeting 20 years ago, during a Mother’s Day event at his Mar-a-Lago estate in Palm Beach, Florida.
A spokesman for Mr Trump rejected the claim.
Mr Trump has denied attacking any of the women who have made allegations against him, saying the claims are part of a plot to damage his campaign.
The final televised debate takes place on Wednesday.