GEOFF BENNETT: Welcome to the "News Hour."

It's an historic night that could shape the course of the presidential election now just 55 days away.

Vice President Kamala Harris and former President Donald Trump are set to face off in Philadelphia in their first and potentially final debate.

AMNA NAWAZ: The last presidential debate in June between Trump and President Biden changed the course of the race, so tonight is highly anticipated.

A new PBS News/NPR/Marist poll shows that 70 percent of Americans say they will be tuning in tonight, while another quarter plan on following at least some coverage.

GEOFF BENNETT: And while a majority of Americans say they don't believe a debate will impact their vote, nearly a third say the matchup could influence their pick for the top of the ticket.

We have got a full table here in the studio for analysis of what's at stake.

The gang is all here.

With us all night, Amy Walter of The Cook Political Report With Amy Walter, Democratic strategist Ameshia Cross, and Republican strategist Kevin Madden.

Welcome to the three of you.

So, Amy, I know you're particularly interested in who is paying attention to this debate tonight, this poll... AMY WALTER, The Cook Political Report: That's right.

GEOFF BENNETT: ... that nearly a third of voters say that this could be determinative for them is they make a decision about who they're going to vote for.

AMY WALTER: That's right.

And, normally, we think of debates as not having that -- especially a fall debate, that much influence on the course of the campaign because voters up until this time have seen a lot of these candidates.

They watch them through the primaries, they have seen them go back and forth.

That's not the case now.

Of course, Harris, the vice president, is pretty new to a lot of people, especially to folks who are younger or voters of color.

So when the Marist poll asked, will this debate affect your vote for president, a little over half of Black voters, 45 percent of Latino voters, and 44 percent of the youngest voters, those Gen Z and millennials, say that it will.

It's also important to note that these are the voters that right now Harris has had some trouble reconstituting into the Democratic sort of constituency that Biden had in 2020.

GEOFF BENNETT: And, Ameshia, for Kamala Harris, the challenge tonight is to address those voters who say they don't know enough about her, they don't know enough about her policies, they're skeptical as to whether or not she can be an agent for change.

How does she make the best use of her time on the debate stage tonight?

AMESHIA CROSS, Democratic Strategist: I think that she has to create that contrast.

She has -- and not just with former President Trump, but also with the policies that came out of the Biden administration that some younger voters and voters of color in particular were not exactly excited about.

So she's got to move forward in things like economic development, talking about job creation and jobs that provide more than a living wage, talk about housing affordability, talk about small business and small business growth, particularly because, for Black women, that is where their funds are coming from.

It is not necessarily jobs in the job market as much as it is they're creating their own.

So when she's talking about those economic policies, that is part of the agenda.

The other thing is she's got to talk about things like Project 2025 and how detrimental that is to various demographics, but most importantly also bringing in those younger voters, because before they were a part of that double hater group.

They didn't want to see either candidate.

They thought they were too old.

At this point, they're still tying her, some of them, to the Biden administration in ways that aren't necessarily the most helpful.

She's got to show a progressive vision for the future for them as well.

GEOFF BENNETT: And, Kevin, Donald Trump, according to his aides, hopes to cast Kamala Harris as being too liberal, trying to tie her to the Biden administration's unpopular policies.

His aides say that they hope he can stay on message.

We know Donald Trump is loose with the facts and quick with an insult.

What does a successful night look like for him tonight?

KEVIN MADDEN, Republican Strategist: Well, look, I think we're talking about defining the candidates.

Donald Trump, there's really not much room for definition, right?

I would say he has 100 percent name I.D.

and you might even say 110 percent.

People have very fixed opinions about him.

But this is essentially a contest to try and define Kamala Harris in the eyes of swing voters.

So I think that is exactly what we're going to expect tonight is to see Donald Trump come out in a very aggressive fashion, try to paint Kamala Harris as a West Coast liberal, not a progressive, but a West Coast liberal who's out of step with them on the issues that they care about.

And I think the issues are exactly as Ameshia had mentioned.

It's housing, it's inflation, childcare costs, those type of things.

So I think that's really what his core goal is tonight is to define Kamala Harris for these swing voters.

AMNA NAWAZ: Well, let's turn to our own intrepid reporters to weigh in on this who will also be with us all night.

Of course, Lisa Desjardins is covering the Trump campaign.

Laura Barron-Lopez covers the Harris campaign for us.

So, Laura, let's start with Vice President Harris here.

She's had less recent debate experience than former President Trump.

What do we know about how she's preparing for tonight?

LAURA BARRON-LOPEZ: The vice president spent roughly five days or so in Pittsburgh, Pennsylvania, before heading to Philadelphia yesterday, only briefly stepping out to visit local businesses.

She was hunkered down preparing for this debate over the course of those days.

And I was told by sources familiar that Philippe Reines, a longtime aide to Hillary Clinton, played Donald Trump during that debate prep, so reprising his role, because he did that as well when Hillary Clinton ran for the presidency.

And campaign sources also told me that they view this format as one that benefits Donald Trump, that Vice President Harris expects the showman to show up tonight.

And she's been preparing for that.

Also, President Biden spoke to the vice president today, saying that he wasn't going to tell reporters what advice he gave her, but that she was calm, cool, and collected, and he will be watching the debate later tonight.

AMNA NAWAZ: Lisa, what about the former president?

We know his allies love to say that Donald Trump does not do debate prep.

Obviously, he prepares in some way.

What do we know?

LISA DESJARDINS: He does do debate prep.

You just can't call it debate prep.

AMNA NAWAZ: OK. LISA DESJARDINS: It is actually an inside joke within the campaign.

Multiple campaign sources tell me to call it policy time.

What happens is, you sit down with Donald Trump at a table and you go oh, not just Kamala Harris' policies, proposals, and past, but also Donald Trump's, to make sure that they hone what he's going to say, how he wants to summarize them, and that he understands all the policies thoroughly that could come up.

Now, there is not a mock debate situation.

There really couldn't be more of a contrast in the way these two campaigns are doing this.

And the former president was at Mar-a-Lago for most of today.

He wasn't in the state.

He traveled to the debate today.

But he is getting some help from some sort of big names within the conservative circles.

Look at two that are helping him prepare, Representative Matt Gaetz there from Florida and Tulsi Gabbard, former Democrat.

Matt Gaetz is not portraying Kamala Harris, but he is the one pushing tough questions to former President Trump, challenging him back and forth.

Now, Tulsi Gabbard, why is she there?

I was told she's there to give insight.

And then a top campaign source told me, more frankly, you can't have a discussion about a debate with Kamala Harris with just seven guys in the room.

So they wanted a woman, and Tulsi Gabbard is the woman.

AMNA NAWAZ: So, Laura, what is Vice President Harris' plan for this debate?

What's she hoping to accomplish tonight?

LAURA BARRON-LOPEZ: Sources inside the campaign and sources close to the campaign told me that Harris views this as one of the biggest chances to speak to those voters that Amy and Kevin and Ameshia were talking about, which was those undecided voters, the sliver of them that are still left, be it the disenchanted Republicans or the young voters that she needs to come home, rather than sit out the race.

And to give an idea of who she believes she needs to focus, speaking of those disenchanted Republicans, two of the surrogates that they have there at the debate are two former Trump administration officials, Anthony Scaramucci and Olivia Troye.

And then, when it comes to creating big moments during this debate, I was told by sources that she's going to go on offense on abortion and reproductive rights and really try to anchor Trump to that and highlight his flip-flops on the issue.

She may very well actually highlight voices of women and physicians that have been impacted in those states with abortion restrictions.

On inflation and affordability, Harris may try to differentiate herself from President Biden on that issue by showing a bit more empathy.

Democrats admitted that President Biden at times would get really defensive about the economy, given the good data points, and that she will try to say that she understands how people are feeling with high costs and inflation.

And then she's also going to look for moments to get under his skin, I'm told.

And one thing to watch as well, according to my sources, is that she may try to goad President Trump on election denial specifically, speaking potentially directly to him, saying that he lost and trying to get him to admit that he lost.

AMNA NAWAZ: So, Lisa, is the Trump campaign preparing for that kind of goading?

I mean, what do we expect to hear from the former president?

LISA DESJARDINS: They are all hoping for, and people have probably seen this reporting elsewhere too, as I'm told, happy Trump, calm, happy Trump.

They know the Harris campaign strategy is to try and get under his skin.

That said, it is Donald Trump.

He is someone who it is hard for him not to react when attacked.

He thinks he's better at attacking and he thinks he's got that power.

So they're trying to tell him, look how well you did with President Biden.

Keep that kind of approach here tonight.

However, there are some topics that they're nervous about.

Project 2025 is something that does get under former President Trump's skin.

It's something he's disavowed, but we know that it is many of his former and current advisers that are part of that.

That's something they're nervous about.

What does he want to go in offense about?

Well, the one topic phone call that the Trump campaign had today was on crime and border.

That's something where they think that they can make a better case.

They will also probably accuse Vice President Harris of telling lies.

That's something he's been accused of.

He's going to try and turn that around tonight in the debate.

GEOFF BENNETT: Ameshia Cross, that reporting that Laura shared that the Harris campaign believes that this is a format that benefits Donald Trump, that struck me as interesting because you could argue that Kamala Harris, there's a lot of upside for her tonight, in that she gets to redefine herself for some voters and introduce herself to others, whereas views of Donald Trump by this point are fairly calcified.

How does she do it?

AMESHIA CROSS: Oh, no, absolutely.

I think that she has to do both of those things effectively.

But the other thing that she has to do, which has been proven very difficult no matter who Donald Trump is debating against, is fact-checking in real time.

Without a -- without the mics being open, she can hear the jeers and the side comments and everything he's saying, but she's not going to be able to reply to them in real time where people can actually hear what he said.

She's got to create a time and a space to call him out on his lies, not all of them.

The man lies 500 times a minute.

She's not going to be able to do that.

But she also has to, in that same vein, not just talk about what Trump is for, but also what a Kamala Harris administration would look like and the progress that she plans on making for the demographics that are still a little bit on the fence.

Again, I think that's a much smaller slither of the American population, but this is going to be a race that is decided within the margins.

So she's got to define herself.

She's also got to plaster him for who he is and what he stands for.

She's also got to appear to not fall into the angry Black woman trope, because that is what Donald Trump is going to try to bring out of her.

GEOFF BENNETT: And, Kevin, Lisa's reporting that the Trump campaign is trying to focus on crime and immigration, taking Ameshia's point that this is an election that's going to be decided at the margins, are those two issues resonant enough to make a difference in this election?

KEVIN MADDEN: Well they are, because I think, if you look at where this campaign is going to be litigated at the margins, which is the seven battleground states and the population centers around there, so if we're looking at suburban Philadelphia, suburban Atlanta, suburban Phoenix, immigration and crime are very big issues.

Those are issues where Donald Trump can -- and what I expect him to do is really try to -- really try to sort of confront Kamala Harris on the Biden record and tie her to the Biden administration and people's perceptions about the Biden administration being very weak on both of those issues, because that's where Kamala Harris has really probably made the most gain over the last 60 days, is that she, as becoming the new candidate in the race, she was the only candidate not named Trump or Biden.

So people were sort of euphoric about that.

But -- and she got the mantle of change.

Trump has to sort of take that away from her, tag her a little bit with the incumbency, and then talk about those issues, about what he would do to chart a different course for those voters that care about it.

GEOFF BENNETT: Amy, what makes this election different for Democrats is that they have an enthusiasm advantage, something they didn't have in 2020, something they didn't have in 2016.

How do they sustain that in the 55 days to go?

AMY WALTER: Well, I would argue that they have that same amount of enthusiasm advantage that Republicans have right now.

I think both sides are equally engaged.

The challenge right now for Harris is that she's gotten all of those people who are the most engaged, but she still needs to get a sliver of those people who right now feel like they don't know her that well, they don't know if voting is as important to them as it was maybe in 2020, or that they weren't part of the electorate in 2020 and have to be convinced that this is important for them to show up.

GEOFF BENNETT: Well, thank you to our correspondents and our analysts.

We will have live special coverage of the debate right here starting at 9:00 p.m. Eastern.