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.

TRUMP'S CLAIM: "And now, we're weeks away from a vaccine."

FACT CHECK: Most prominent public health experts have said that a vaccine will not be widely available until mid 2021.

The pharmaceutical company Pfizer has said they may have data from its late-stage trial by October. Moderna has said it could have data from its late-stage trial by November or December. From there, the data will need to be analyzed by the FDA to determine whether the vaccine is both safe and effective. Other companies in late-stage trials are further behind. AstraZeneca's late stage trial is still on hold, and Johnson and Johnson only just started its late-stage trial this month.

Even if a vaccine is authorized by the end of the year, that does not mean it will be widely available. At first, only limited supplies will be available, and they will be prioritized for the most vulnerable.

"By the time you mobilize the distribution of the vaccinations and you get the majority or more of the population vaccinated and protected, that's likely not going to happen until the mid- or end of 2021," Dr. Anthony Fauci, the nation's top expert on infectious diseases, told MSNBC's Andrea Mitchell earlier this month.

In a recent Senate hearing, CDC Director Robert Redfield echoed those sentiments, "I think there will be vaccine that will initially be available some time between November and December, but very limited supply, and it will have to be prioritized," but, he said, "If you're asking me when is it going to be generally available to the American public so we can begin to take advantage of vaccine to get back to our regular life, I think we're probably looking at late second quarter, third quarter 2021."

-- ABC News' Sony Salzman