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

In the wake of that canceled second showdown and a chaotic first debate before it, the Commission on Presidential Debates announced earlier this week it would mute candidates’ microphones at certain points Thursday to avoid interruptions and “maintain order.”

Trump and Biden will now have two minutes each of uninterrupted time to speak at the beginning of each 15-minute segment, of which there are six, in the 90-minute debate.

After the first four minutes of each segment, both of their microphones will go live for an “open-discussion portion,” the commission co-chair said. The moderator will not have control of the candidates' mics at any point. Those will instead be controlled by event production staff.

ABC News Chief Congressional Correspondent Mary Bruce said on ABC News Live Prime ahead of the debate, “Just because your microphone is down, doesn't mean that you necessarily will stop talking.”

Trump has attacked the integrity of the debate commission and its chosen moderators in recent weeks, deeming it all "crazy" and the new mic rule "very unfair” -- but sources have told ABC News Chief White House Correspondent Jonathan Karl that some advisers think muting the mics will actually help the president.

Biden, meanwhile, has called the muting of mics "a good idea" and said he’s expecting Trump to fire off personal attacks during their final showdown.

ABC News Chief Anchor George Stephanopoulos said the big question for Biden, who leads in nationwide polls, is whether he can close the deal with voters from Nashville. For Trump, it's how will he adjusts his performance after the "disastrous" first debate more than three weeks ago.

"Even the president's own aides called his blustering performance a self-inflicted wound," Stephanopoulos said.