Democrat Hillary Clinton and rival Donald Trump
waded into their last presidential debate Wednesday with the Republican candidate spiraling downward in the polls amid allegations of sexual misconduct and wild charges of a "rigged" US election.
With less than three weeks to go before Americans cast ballots on November 8, polls showed Clinton widening her lead over the Republican nominee.
The 90-minute debate at the University of Las Vegas, Nevada was expected to offer Trump what may be his last chance to turn around a campaign that has been battered by a stream of allegations he groped and forced himself on women.
"We've only just begun to fight, believe me," Trump said while campaigning in Grand Junction, Colorado Tuesday. "This is our final shot, folks."
Clinton has kept a low profile in recent days, shutting herself in with aides at a hotel near her home in Chappaqua, New York to prepare for the third televised debate.
Both candidates on Tuesday jetted separately into this gambling and entertainment capital in the Nevada desert ahead of the high stakes encounter.
Moderated by Fox News journalist Chris Wallace, the event was set to begin at 1 am GMT, before a televised audience expected to number in the millions.
The candidates will be asked about the debt and entitlements, immigration, the economy, the Supreme Court, foreign flashpoints and their fitness to be president.
The past two debates quickly degenerated into highly personal, mudslinging attacks that pushed substantive policy issues to the side.
Clinton "should do what she did in the two first debates which was largely remain calm, deflect criticism and attacks and let Donald Trump continue to self destruct," said John Hudak, a senior fellow at the Brookings Institution.
"If your opponent's ship is sinking you don't throw them a life preserver," he said.
Trump undoubtedly will draw on the lessons of the past two debates, and sharpen his attacks on Hillary over Syria and Libya.
The jihadist attack on the US diplomatic mission in Benghazi, Libya on September 11, 2012 remains a burning issue among Republicans, who hold the former secretary of state partially responsible for the deaths of four Americans, including the ambassador.
Trump has invited Patricia Smith, the mother of a communications expert killed in the Benghazi attack, to attend the debate, according to Yahoo News.
During the last debate, he invited four women, three of whom had accused former president Bill Clinton of sexual assault.
An average of recent national polls shows Clinton with about 46 percent support to 39 percent for Trump and 6.4 percent for Libertarian candidate Gary Johnson.