Donald Trump and Joe Biden hold a high-stakes debate tonight that may be the final opportunity for the president - trailing in the polls - to present his case for re-election to a prime time American television audience of millions. 

Mr Trump, 74, is expected to use the second and last debate to renew his attacks on the past business dealings of Mr Biden's son Hunter. 

Joe Biden, 77, is expected to focus on President Trump's handling of the coronavirus pandemic which has left more than 222,000 people dead in the United States and millions unemployed. 

With the election just 12 days away, the debate is being seen as perhaps Mr Trump's last and best chance to make up ground on Mr Biden before the 3 November vote. 

More than 45 million Americans have already cast their ballots, according to a University of Florida tally, and the candidates will be targeting any remaining undecided voters. 

"This is an important last opportunity for the candidates to talk to people who haven't voted," said Amy Dacey, executive director of the Sine Institute of Policy and Politics at American University. 

"This is probably one of the largest audiences they'll reach right before the election," Ms Dacey said. 

"I think the Trump team must be looking at this as a must to reach people and convince people," said Ms Dacey, a former chief executive officer of the Democratic National Committee. 

Kyle Kondik, managing director of the political newsletter "Sabato's Crystal Ball" at the University of Virginia Center for Politics, said the debate is the final major event on the road to the election. 

"Donald Trump went into the conventions trailing, and he is still trailing," Kondik said. "The debate represents one of the last opportunities to change the trajectory of the race. 

"The stakes are high for both candidates though - Biden wants to keep the race just where it is, and he doesn't want to provide any late fuel to the Trump campaign." 

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'Bias, hatred and rudeness' 

Donald Trump trails Joe Biden by 7.7 points in a RealClearPolitics average of national polls and is behind in most of the key battleground states that are crucial to victory. 

The 90-minute debate is being held at Belmont University in Nashville, Tennessee, and is scheduled to start at 9:00 pm Eastern Time (0100 GMT). 

It will be televised by all the major broadcast networks, cable news channels and live-streamed on various platforms including YouTube. 

The first debate on 29 September was a chaotic affair with constant interruptions and name-calling and measures have been put in place this time to try to ensure order. 

The candidates' microphones, for example, will be cut off while the other one answers questions from the moderator. 

A second debate planned for 15 October was cancelled after Mr Trump came down with Covid-19 and declined to take part in a virtual debate. 

As a health precaution, plexiglass barriers have been erected this time alongside the lecterns where the two candidates will stand. 

The topics for the debate were picked by the moderator, Kristen Welker, a White House correspondent for NBC News. 

Ms Welker, 44, the first woman of color to moderate a debate since 1992, selected six topics: fighting Covid-19, American families, race in America, climate change, national security and leadership. 

Mr Trump has lashed out at Ms Welker on several occasions, calling her a "radical Democrat" and "no good". 

He took another shot at her on Thursday as the White House released raw footage of an interview Trump did with the CBS show "60 Minutes". 

"Look at the bias, hatred and rudeness on behalf of 60 Minutes and CBS," Trump said. "Tonight's anchor, Kristen Welker, is far worse!" 

In the "60 Minutes" interview Mr Trump also continued to fling accusations of corruption at the Bidens - a line of attack he is likely to pursue during the debate. 

"It's the biggest scandal," Mr Trump told 60 Minutes, an assertion met with skepticism from the CBS interviewer. "I think it's one of the biggest scandals I've ever seen and you won't cover it." 

The debate comes a day after former president Barack Obama hit the campaign trail for Biden, delivering a scathing takedown of Trump and urging Democrats to not be lulled into complacency by his former vice president's lead in the polls.

Obama issued a stark reminder of 2016, when surveys showed Hillary Clinton as the clear favorite - only for her to lose to Donald Trump on Election Day.

The debate will be broadcast live on the RTÉ News channel from 2am tomorrow morning and repeated at 9am.