LAS VEGAS: Democrat Hillary Clinton and rival Donald Trump face off for their last presidential debate on Thursday (today) with the Republican candidate spiralling downwards in the polls amid allegations of sexual misconduct and wild charges of a “rigged” US election.

With just 20 days before Americans cast ballots on Nov 8, polls showed Clinton widening her lead over the provocative billionaire.

The 90-minute debate at the University of Las Vegas, Nevada offers Trump what may be his last chance to roll the political dice and reverse a campaign that has been battered by a stream of allegations he groped and forced himself on women. “This is our final shot, folks,” Trump told supporters on Wednesday in Colorado.

Clinton has kept a low profile in recent days, shutting herself in with aides to prepare for the third televised debate of the campaign.

The past two debates quickly degenerated into highly personal 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.

The 2012 jihadist attack on the US mission in Benghazi, Libya 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 an American killed in the attack, to attend the debate, as well as President Barack Obama’s Kenyan-born half-brother Malik, who supports Trump, campaign manager Kellyanne Conway said.

The move is a clear ploy to rattle the former secretary of state, much like Trump sought to do in the previous debate when he invited women who had accused former president Bill Clinton of past sexual misconduct.

New allegations emerged on Wednesday, from a former reporter who claims Bill Clinton groped her in 1980 when he was governor of Arkansas — potentially providing new fodder for Trump to attack the Democratic nominee over her husband’s past.

Trump is likely to hammer Clinton over recent revelations from emails hacked from her campaign staff and released by WikiLeaks that exposed her closed-door speeches to Wall Street and showed her deliberations over free trade.

An average of recent national polls shows Clinton with a seven point lead over Trump when the race includes third-party candidates Gary Johnson and Jill Stein. Trump predicts an electoral surprise, or “new Brexit,” when Americans vote next month.

But as he’s lost ground, the New York real estate mogul has attacked the election process itself, complaining of a conspiracy to steal the election from him. “The press has created a rigged system and poisoned the minds of the voters,” he said on Tuesday. “Either we win this election or we lose the country.”