Trump's advisers have urged him to highlight his policy differences with Biden and present his case to the American people as to why he deserves another four years in office, sources said.

He trails Biden in the polls and this is his final opportunity to pitch himself to a large audience in primetime before Election Day.

Some top advisers would like to see a less combative, calmer Trump at the debate but concede that is an uphill battle given the president will focus on Biden’s family, which aides hope will get under Biden's skin, multiple sources said. However, other top advisers don't think that focus helps move any of the remaining swing voters. 

Aides have also urged him not to interrupt Biden as much and have been re-watching the last debate with Hillary Clinton in 2016 as a guide as the White House views that debate as his strongest. The president's team also intends to heavily monitor the mute button usage, sources said. 

Trump has held no mock debates leading up to his final face-off with Biden and has prepped -- in what one source described as a "very compartmentalized" way -- with different subject matter experts providing the president a briefing and preparing notes for the president on a particular topic. He has said his best preparation comes from his exchanges with the press.

The group advising the president has also slimmed down. For example, his former counselor Kellyanne Conway and former New Jersey Gov. Chris Christie have taken less prominent roles.

-ABC News’ Katherine Faulders, John Santucci and Will Steakin

As he boarded his plane to Nashville earlier, Biden spoke briefly with reporters, telling them he's looking forward to the debate and said he hopes Trump plays by the rules.

"There's plenty of time to talk when this is over, OK? So hopefully he's going to play by the rules. Hopefully everyone's been tested. Hopefully it's all worked out, the way the rules are. I'm looking forward to this," Biden said before getting on the plane.

Biden's team has remained tight-lipped about their debate preparation for the final debate, but allies and advisers to Biden said they aren't expecting much of a change from either candidate ahead of the crucial matchup.

"I think Joe Biden is prepared for a completely unconventional debate in which the President of the United States does not act presidential (for) one minute. And the challenge is to not be distracted by the Trump show, and to make sure that Joe effectively puts out his positive vision," Sen. Chris Coons, D-Del., told ABC News.

An aide to Biden said the former vice president plans to again focus on his message to viewers at home, but would not be shy about standing up to Trump's interjections when necessary, especially given reports of the president's planned personal attacks on Biden and his family.

-ABC News' Molly Nagle

The debate between Trump and Biden will run from 9 p.m. to 10:30 p.m. with no breaks for commercials.

The program will be divided into six segments of 15 minutes each with topics decided by the moderator, NBC News White House Correspondent Kristen Welker.

Topics for Thursday’s debate are:

The debate commission has removed the two plexiglass barriers that were positioned between the candidates' lecterns.

Peter Eyre, senior advisor with the Commission on Presidential Debates, said that circumstances on the ground have changed and it's unlikely that the plexiglass partitions will be put back up, according to a pool report.

The news follows both candidates reporting testing negative for COVID-19. It's unclear if those who accompanied them to travel to Nashville were also tested.

-ABC News' Drew Millhorn

TRUMP'S CLAIM: "The children are brought here by coyotes and lots of bad people, cartels, and they're brought here and they used to use them to get into our country." // "They built cages. You know, they used to say I built the cages." // "They are so well taken care of. They are in facilities that are so clean."

FACT CHECK: Trump was defending his now-defunct policy known as "zero tolerance" that required every adult who crossed the border illegally -- even those traveling with their children -- be detained in a bid to deter border crossings.

The result was that thousands of children were separated from their parents in a matter of weeks. It was a major departure from past U.S. policy. In the Barack Obama and George W. Bush administrations, families were separated in rare instances, such as cases of serious crimes like drug trafficking. 

Critics of Trump's policy questioned the conditions the kids were kept in initially at border stations after several died of the flu.

An internal investigation later found that the administration struggled to keep track of the parents, many of whom had been deported. The White House says the parents were contacted and abandoned the children, who were placed with U.S. sponsors, usually family members. The American Civil Liberties Union countered that parents have not been found and contacted and therefore could not give up rights to their children.

Homeland security officials have said that "coyotes" are often used to transport the families for a fee. But there has not been widespread evidence of cases of people falsely presenting themselves as related, with border patrol documenting them as "family units."

Trump's suggestion that "cages" were built by the Obama administration is correct. Obama had faced an influx of children both traveling alone and with families as a result of violence in Central America. And at one point, the Obama administration tried housing the families in special detention centers.

But after a federal judge in California ruled that the arrangement violated a long-standing agreement barring kids from jail-like settings for extended periods, even with their parents, the government began releasing families into the U.S. pending notification of their next court date.

In 2018, photos taken by The Associated Press and posted online by liberal activists suggested the children in steel fencing was Trump's doing. The photos were actually from 2014 when immigration detentions became flooded with families.

-ABC News' Anne Flaherty