Harris and Trump will need to navigate the pitfall-filled debate of their political lives as each tries to persuade millions of voters and viewers that they're the one best suited to be president.

Harris, whose wave of momentum has brought Democrats back to a neck-and-neck presidential race, will have to prosecute the case against Trump while also laying out how her agenda could help the country -- particularly beleaguered middle- and working-class Americans.

Trump, meanwhile, has the task of casting his record on the economy and immigration as superior to Harris' while avoiding distracting personal attacks on Harris.

Republicans and Democrats told ABC News how they should meet the crucial moment. Read more here.

-ABC News' Tal Axelrod

How much difference do presidential debates make? In the past, they've rarely influenced an election's outcome, according to historians who spoke with ABC News.

But the June debate between President Joe Biden and former President Trump was a rare exception, they say, ultimately leading to an unprecedented change in the Democratic presidential ticket.

Now as Vice President Harris prepares to take on Trump in their first presidential debate, experts predict the matchup could potentially produce a similar consequential and history-making moment that could sway undecided voters -- a key voting bloc that could determine who wins the November election.

Read more here.

-ABC News' Ivan Pereira

A recent New York Times/Siena College poll found a sizable share of likely voters (28%) and registered voters (31%) feel they need to know more about Harris as a candidate. Those numbers were even higher among independent voters: 41% of registered independents and 38% of likely voters who identified as independent said they needed to learn more about her.

Her campaign is well-aware that a large slice of the critical voting bloc feels they don't know Harris well enough, ABC News Chief White House Correspondent Mary Bruce reports.

Tonight, she'll want to fill in the blanks in what is her highest-profile appearance since her acceptance speech at the Democratic National Convention last month. But beyond that, their real goal is to make clear the stark choice in this election between what she wants to do as president and what Trump intends to do.

The Harris campaign released its list of surrogates who will be in the spin room during the debate.

Four Democratic governors -- Roy Cooper of North Carolina, Michelle Lujan Grisham of New Mexico, Gavin Newsom of California and Josh Shapiro of Pennsylvania -- are among the group, as well as Sens. Laphonza Butler of California, Tammy Duckworth from Illinois and Chris Murphy of Connecticut.

Four Democratic House members -- Jason Crow from Colorado, Veronica Escobar of Texas, Robert Garcia from California and Ted Lieu of California -- will also be joining, as well as retired Brig. Gen. Steve Anderson, a former Republican; Reproductive Freedom for All President and CEO Mini Timmaraju and Khizr Khan, a Gold Star father.