PITTSBURGH Ninety minutes Tuesday night may well offer newly anointed but still relatively little-known Democratic presidential nominee Kamala Harris her last and best chance to define herself for voters, even as Donald Trump tries to do it for her.

The vice president has managed to consolidate most of her partys voting coalition in the seven weeks since President Joe Biden abruptly ended his reelection campaign and threw his support behind her. But her failure to lock down some groups, such as young Black men and Latinos, has left her campaign in a precarious position against the coup-attempting former president with less than two months left until Election Day.

The challenge for both, in a sense, is to define Harris, as Trump is well-known, said David Axelrod, the Democratic consultant who helped Barack Obama win the White House in 2008.

Trump, who has been convicted of 34 felony counts, has spent the duration of her presidential candidacy attacking Harris as a Marxist and communist who holds extreme views on cultural issues. Harris has emphasized her rsum as a prosecutor and Californias elected attorney general in her attempt to portray herself as a pragmatic centrist.

Recent polling shows that, despite both of their efforts, a significant percentage of Americans say they dont really know much about her. A recent New York Times survey found that 28% of likely voters say they need to know more about Harris, while only 9% say the same about Trump.

One Republican consultant who has worked on multiple presidential campaigns, who spoke on condition of anonymity, said he cannot think of a higher-stakes confrontation in the history of modern presidential races.

Im not sure I have enough wine handy tomorrow to get me through this debate, he said. I think it could be a complete game changer. Its going to be the single most important debate after the previous single most important debate that got Biden bounced.

Tuesdays contest was initially supposed to be the second one between Biden and Trump. That matchup ended, though, in the weeks following Bidens disastrous performance in their first debate of the 2024 election cycle, on June 27. Biden sounded hoarse and looked weak, which his campaign blamed on a cold, and flubbed questions, reinforcing many voters concerns about his age. At one point, he said he finally beat Medicare when he meant to take credit for beating the pharmaceutical industry.

Bidens polling numbers cratered in the days and weeks to come, as did his fundraising, and prominent supporters urged him to drop out. On July 21, he announced on social media that he was ending his reelection campaign and followed up shortly with another post endorsing Harris for the nomination.

Tuesdays debate will be hosted by ABC News at the National Constitution Center in Philadelphia but will be simulcast by most other broadcast and cable networks. It is scheduled to begin at 9 p.m. EDT.