The last time former President Donald Trump was on a debate stage, he ended President Biden’s political career.

He will return to the stage Tuesday in Philadelphia, hoping to upend the Democratic Party’s replacement nominee, Vice President Kamala Harris.

The 90-minute affair, hosted by ABC, will give Mr. Trump a chance to force Ms. Harris, who has primarily been avoiding critical media coverage, to face new scrutiny.

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“He’s got one real chance to expose her as a radical liberal, a vapid tosser of word salads, or a continuation of Biden’s disastrous administration — or all three,” said Republican Party strategist Scott Jennings. “He’s got to push her into a different frame, and the debate is the place to do it.”

Mr. Trump has been here before. He faced off in debates against Hillary Clinton in 2016 and Mr. Biden in 2020, and in June when he dealt the final blow to the president’s reelection hopes.

Ms. Harris has never been in a head-to-head presidential general election debate, though she participated in debates with fellow Democrats as part of the 2020 primary process.

Her job on stage will be to take credit for achievements of the Biden agenda while ducking responsibility for unpopular aspects, such as inflation, and trying to keep the focus on the deeply divisive Mr. Trump.

“Is the campaign a referendum on the Harris/Biden years of inflation and economic disappointment?” said Larry Jacobs, director of the University of Minnesota’s Center for the Study of Politics and Governance. “Is the campaign a referendum on Trump and returning to the economic decline of 2020 and the chaos of his term?”

Less than two months ago, Mr. Biden, under pressure from Democrats, pulled out of the race after his disastrous debate performance against Mr. Trump in Atlanta. The debate revived concerns about the age and cognitive ability of the 81-year-old president, prompting party leaders to compel him to bow out.

Since then, Mr. Trump has survived an assassination attempt and named Sen. J.D. Vance of Ohio as his vice presidential nominee. Ms. Harris was tapped to replace Mr. Biden and brought on Minnesota Gov. Tim Walz as her running mate.

The shake-up has energized Democrats, as evidenced by Ms. Harris’ massive $361 million fundraising haul last month, and the polls have tightened dramatically.

Eight weeks from Election Day, Mr. Trump and Ms. Harris both have a clear path to the presidency, according to polls showing a tight race in the swing states of Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.

On the issues, polls show Mr. Trump is more trusted to handle the economy, immigration and, in most cases, crime. Ms. Harris has the upper hand on abortion and protecting democracy. She is also viewed as a less extreme, more unifying and more caring figure.

In the debate, Ms. Harris seeks to reinforce those positives, remind voters of her experience as a prosecutor and convince voters she can be a steady leader who thinks independently.

Political pros said they are waiting to see whether Mr. Trump or the moderators will force her to go beyond talking points.

“When she goes off script, she is a train wreck,” said Chris Ager, chair of the New Hampshire Republican Party. “Her best strategy is the Biden basement strategy: Stay the hell away from an open mic.”

Mr. Trump shares that view. He figures the more the public sees and hears from Ms. Harris, the less they will like her.
“Nobody knows who she is,” Mr. Trump said.

He has argued that Ms. Harris deserves blame for much of what alienated voters from Mr. Biden. He has been hammering home the idea that Ms. Harris is a “communist” and a “radical.”

“She can’t talk, and they are not going to skate through,” Mr. Trump said at a recent press conference. “We are not going to have a Marxist present. The people are getting it.”

A debate wasn’t always certain.

In 2022, Republicans withdrew from the commission that had sponsored debates for decades. Mr. Trump reached an agreement with Mr. Biden earlier this year to hold two debates, each tied to a major news outlet.

After the June debate, hosted by CNN, proved fatal to Mr. Biden’s campaign, Ms. Harris and Mr. Trump began sparring over the next showdown. Mr. Trump complained about ABC and suggested other debates with other outlets.

Ms. Harris held firm, and Mr. Trump, desperate to force more scrutiny on his opponent, agreed to the debate.

The campaigns have agreed to forgo notepads. The candidates will be standing, and the microphones will be muted when it is not their turn to speak.

Harris campaign members wanted the unmuted microphones because they thought Mr. Trump could self-destruct from a lack of impulse control.

On Friday, Mr. Trump tried to downplay expectations by saying that ABC News is biased against him.

“I’m going into very hostile territory in a debate with ABC. ABC is the worst of everybody. They are the nastiest. As bad as you can be.”

Ms. Harris has been preparing for the showdown with Karen Dunn, a lawyer and longtime Democratic operative, and Rohini Kosoglu, a trusted aide who served as her chief policy adviser during her term as vice president, on her failed 2020 presidential campaign and in her Senate office.

Mr. Trump has received help from former Rep. Tulsi Gabbard, who debated Ms. Harris in the 2020 Democratic primary race. She endorsed Mr. Trump last month.