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: "Nobody knew where it was coming from, what it was. We've learned a lot. But Anthony said don't wear masks. Now he wants to wear masks."

FACT CHECK: Dr. Anthony Fauci, one of the top infectious disease experts in the country, and other public health experts initially told Americans not to wear surgical or N95 masks in the early days of what has become the COVID-19 pandemic.

At the beginning of the pandemic, the Centers for Disease Control and Prevention and the World Health Organization, as well as Fauci and other top experts, initially discouraged wearing masks because of concerns that masks and other personal protective equipment were in short supply for health care workers who needed them. Public health officials were also concerned wearing masks could have unintended consequences if people touched their face more often to adjust them or fail to keep social distancing.

"There was this feeling that there would be a shortage just for those who really need them very early on," Fauci said in a recent interview. "That was the big deal. We didn't have enough PPE including masks. Then it became clear that cloth masks worked reasonably well. And therefore there was no more shortage. Then the different analyses, meta analyses and others came in that in fact, it does work."

In early April, the CDC changed its recommendation about face coverings for the general public, based on evidence that a significant number of people who were asymptomatic or not yet feeling sick were transmitting the virus.

Duke University researchers have also concluded that "if 95 percent of people wear cloth masks when within 6 feet of other people in public, it will reduce COVID-19 transmission by at least 30 percent."

Trump also said he thought Fauci was a Democrat, but Fauci is not registered as a member of any political party, according to D.C. voting records.

-ABC News' Stephanie Ebbs and Arielle Mitropoulos