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.
More personal attacks, by Laura Bicker, BBC News, Washington
Donald Trump’s personal attacks on Hillary Clinton are on the increase.
He’s nicknamed her Crooked Hillary, said he would put her in prison if he was elected president, described her as not having the stamina for the job and now he has accused her of taking some kind of drug.
His rally speeches have become increasingly agitated and he has stepped up his rhetoric aimed at casting doubt on the fairness of this election, saying it is being rigged by a corrupt media pushing false allegations and outright lies.
He may be trailing in the polls but he is managing to attract thousands of people to his rallies and raise funds.
Meanwhile the Clinton campaign has hit back against Mr Trump’s contention that women accusing him of sexual assault are part of a scheme to help elect Mrs Clinton president.
Voting was to be encouraged and not “dismissed or undermined because a candidate is afraid he’s going to lose”, Clinton campaign manager Robby Mook said.
Mr Mook said he expected a record turnout because voters could see through what he described as Mr Trump’s “shameful attempts to undermine an election weeks before it happens”.
Some of the women accusing Donald Trump
Kristin Anderson told the Washington Post he touched her through her underwear at a Manhattan nightspot in the 1990s
Summer Zervos was a contestant on The Apprentice in 2006, and said he forced himself on her at a Los Angeles hotel and began “thrusting his genitals” in 2007
Jessica Leeds told the New York Times that when she was 38 he touched her “like an octopus” in the first-class cabin of a flight in the 1980s
Natasha Stoynoff told People magazine that he “forced his tongue through her throat” when she went to interview the Trumps ahead of their first wedding anniversary in 2005
Mindy McGillivray told the Palm Beach Post that when she was 23, he grabbed her bottom at his Mar-a-Lago club in Florida in 2003
Temple Taggart, former Miss Utah, told NBC News he kissed her on the lips in 1997, when she was 21
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.