Former President Donald Trump and Vice President Kamala Harris will meet for their first debate on Tuesday at Philadelphia's National Constitution Center in a showdown that could define the rest of the presidential campaign.

The debate, which begins at 9 p.m. ET, is being hosted by ABC News. There will be no live audience and no opening statements, according to rules the network released last week. The two candidates will have under two minutes to deliver closing statements. 

Harris and Trump won't be able to ask questions of each other. Only the moderators — ABC's David Muir and Linsey Davis — are permitted to ask questions. 

The debate will last 90 minutes and feature two commercial breaks. The candidates will have two minutes to answer questions, two minutes for rebuttals and an additional minute for follow-ups and clarifications. As CBS News previously reported, Harris' campaign agreed to let the microphones remain muted when a candidate isn't speaking. 

A coin flip determined the podium placement and order of closing statements. Trump won the virtual coin toss, ABC News said, and he decided to offer the final closing statement. Harris chose the position on the right, or stage left. 

The rules also state that candidates will stand behind their lecterns for the "duration" of the debate, a rule that may remind viewers of a 2016 debate between Trump and former Secretary of State Hillary Clinton, when Trump left his place to linger near Clinton, a move some viewed as an intimidation tactic.

Candidates aren't allowed to take prewritten notes or props on stage, and they won't receive topics or questions in advance. 

ABC is allowing other television networks to simulcast the debate. CBS News will air the proceedings on the CBS broadcast network and the streaming network CBS News 24/7.

The debate will be the first time Harris and Trump are meeting face to face.

Aaron Navarro contributed to this report.