1st presidential debate between Trump and Biden spirals into chaotic clash

ABC News' Chief Political Analyst Matthew Dowd predicted the debate may become the most watched event of the 2020 election cycle with upwards of 70 million viewers expected to tune in before offering his strategy on how each candidate should approach the debate.

"I think Joe Biden has to come across as calm, cool, collected and thoughtful. Present his case about why he wants to be president of the United States, prosecute the case against President Trump about what he's done over the last four years and why he thinks it's been not good for the American public," Dowd said.

Trump, on the other hand, should stay away from a constant attack on Biden, Dowd said. 

"The best thing for Donald Trump is to present the reason why his presidency has been good for the American public. Present it in a way that rehabilitates his image because that's the biggest thing that's holding him back right now. It's not the perception of Joe Biden. It's the perception of Donald Trump," Dowd said. 

Noting about 14% of Americans still identify themselves as undecided voters, Davis asked Dowd who's the real target audience tonight -- and if this debate will change much.

“Right now, Donald Trump comes into this, by all accounts, seven or eight points behind nationally, behind in every key target state in the electoral college, so Donald Trump has to move those voters. Joe Biden has to reassure his voters that are with him already and try to speak to some of those small segment of undecided voters,” he said.

Dowd noted analysts deemed Hillary Clinton the winner of the 2016 debates, although it was Trump who ultimately won the race, but he said this election cycle presents a “huge difference” from 2016 as it’s not a race about choice but a referendum.

ABC News Chief Anchor George Stephanopoulos has kicked off the network's live coverage of the first presidential debate of 2020 between Trump and Biden. 

The debate will run commercial free for 90 minutes on ABC and ABC News Live.

Ahead of a campaign stop Tuesday night in Lancaster, Pennsylvania, Vice President Mike Pence sat down for a live interview with Brett Baer on Fox News, where he discussed the upcoming debate. 

"We're literally just counting the minutes from when I know President Donald Trump is going to take our case to the American people and he's going to take the fight straight to Joe Biden. We're going to lay out the contrast tonight," Pence said. 

Looking ahead to how Trump might react to bombshell reporting in The New York Times on his taxes, Pence said the president could instead use Biden's record against him.

"I'm very confident that they took advantage of all of the legal deductions and exemptions that were available in the tax code, and the president tonight may point out the fact that when he was out creating jobs Joe Biden was spending 47 years in Washington, D.C., helping to create that tax code," Pence said. 

Pressed by Baer pointing out that Trump initially called it fake news, but then tweeted that it was "illegally obtained information" along with an explanation, Pence first laughed and then said it is the "same old, same old" allegations before touting Trump's record as a businessman. Pence also said Trump paid millions in state and local taxes but said nothing about federal taxes.

"This is not where the American people are focused," he added. 

The vice president didn't get into any details about his own debate next week against Democratic vice presidential nominee Sen. Kamala Harris but said he's "counting the days."

-ABC News' Justin Gomez

ABC News’ Chief White House Correspondent Jonathan Karl talked through what a typical lead-up to a presidential debate looks like with "ABC News Live Prime" anchor Linsey Davis.

Normally, Karl said a candidate talks about how tremendous a debater his opponent is, hoping to make himself look better during the debate. But Trump’s strategy has been different from years past, trying to downplay Biden instead of build him up.

“For months, Donald Trump has done exactly the opposite -- making it sound like, you know, Joe Biden is somebody who can barely string together a couple of sentences,” Karl said. “So they’ve set the expectations very low, and I think there’s some realization that that is not necessarily a good thing.” 

Davis then asked Karl how prepared Trump is for the debate, and Karl said Trump hasn’t done much debate preparation. However, a top Trump adviser told Karl that facing reporters in the White House press briefing room is like preparing for a debate.