There are no rules requiring Harris and Trump to shake hands before or after the debate.

If they do, it would mark the first time since 2016 that the candidates have shaken hands. Trump and Biden did not shake hands during their two matchups in 2020.

Trump contracted COVID-19 following the first debate.

The two candidates also didn't shake their hands during the June debate.

The Trump campaign during a pre-debate call said Trump is in "good spirits" and will be departing shortly for Philadelphia.

"President Trump is in good spirits. He is currently in Mar-a-Lago. My understanding is that he will be departing shortly to head over to Philadelphia," said Trump campaign senior adviser Danielle Alvarez when asked about his mood going into the debate.

She suggested that the former president is "ready" to talk about inflation, housing affordability and the border among other issues on the debate stage. Alvarez also suggested that Trump might attack Harris for flip-flopping on some key issues such as fracking, police funding and electric vehicles.

"The president is certainly full of surprises. I know that we can expect him to be, you know, with his, his charming self. We know that he is incredible when it comes to weaving in and out of topics -- he's incredible on those policy issues. So that's ... certainly something that may happen," she said.

-ABC News' Soorin Kim, Lalee Ibssa and Kelsey Walsh

Tonight’s consequential presidential debate hosted by ABC News will consist of set rules to govern the matchup, restricting candidates’ speaking time, microphone access, and engagement with campaign staff.

There will be no audience present, and questions will come strictly from the moderators.

After winning the virtual coin flip, former President Trump will offer the final closing statement.

Read more here.

The Harris campaign will fly a drone show over the Philadelphia Art Museum from 8:05 to 8:25 p.m. ET at the famous Rocky Steps, just prior to the debate on Tuesday.

The show will add onto the campaign’s Philly-themed advertising and recent ad mocking Trump and crowd sizes, according to campaign spokesperson Kevin Munoz.

– ABC News’ Gabriella Abdul-Hakim, Fritz Farrow, and Will McDuffie

Fact check: Misleading

The U.S. Capitol Police Office of Professional Responsibility in August 2021 cleared the officer involved in the shooting of Ashli Babbitt, saying that officer would "not be facing internal discipline."

An internal investigation found the actions of the officer were "lawful and within Department policy," it said.

Babbitt was seen on video on Jan. 6 attempting to kick through a window near the House Speaker's Lobby, shortly after Babbitt entered the Capitol. She was subsequently shot and killed by the officer. The agency said they'd reviewed all available evidence in connection with the shooting including video and radio calls, and Capitol Police stood by the officer and said his actions saved the lives of lawmakers and family members.