Donald Trump's campaign manager has acknowledged he may need a "comeback" to win the US election as the candidates prepare for tonight's third and final presidential debate in Las Vegas.

With less than three weeks to go until the 8 November vote, Kellyanne Conway spoke out as a string of battleground state polls put Hillary Clinton ahead.

Speaking to Fox News, she said Mr Trump had pulled off comebacks several times before, suggesting the billionaire would need to do so again - a rare acknowledgement that he might not succeed.

:: Clinton v Trump: Latest polling and battleground states

Meanwhile, Democratic vice presidential candidate Tim Kaine called Mr Trump a "bully" and said he wanted Mrs Clinton to "win big" to put to bed the Republican's claims the election is rigged.


Mr Kaine said he was predicting a "scorched-earth" debate performance from Mr Trump, while Mrs Clinton would be cool and collected in the face of likely insults and histrionics.

Image: Kellyanne Conway pictured with reporters following the second presidential debate

:: Trump invites Obama's half-brother to debate

Ahead of tonight's debate, protesters gathered outside Trump Tower, the hotel gilded in 24 carat gold overlooking the Vegas strip.

One woman told Sky's US Correspondent Hannah Thomas-Peter she was voting for Mrs Clinton as "Donald Trump is bad for this country, he's bad for women and he should not be leading this country".

Another said Mrs Clinton simply had to show up to tonight's debate, stay focused and not get "dragged down" by Mr Trump.

Image: Democratic vice presidential nominee Tim Kaine has called Mr Trump a 'bully'

Mrs Clinton visibly rattled Mr Trump in their first showdown by using his own controversial comments about women and minorities against him.

The businessman was on the defence at the start of the second debate - which came days after the release of a video in which he brags about kissing and grabbing women - but ended on a stronger footing.

With advance voting under way in more than 30 states, at least 2.1 million people have cast ballots already.

This figure is expected to rise to 45 million before election day.

Early balloting has so far shown promise for Mrs Clinton in battlegrounds North Carolina and Florida, while Mr Trump has generally held ground in Iowa and Ohio.

Sky US correspondent Hannah Thomas-Peter speaks to protesters ahead of US debate

Early voting is traditionally favoured by Democrats and is a key part of the Clinton campaign's strategy.

Mr Trump is counting on a stronger performance on election day itself.

Whatever the outcome of tonight's debate, viewers can no doubt expect fireworks.

:: US Election: The Final Debate from 11pm on Wednesday on Sky News. Watch the debate again from 8am on Thursday.