Kamala Harris and Donald Trump will square off tonight at 9 p.m. Eastern for their first, and likely only, debate during this unusually compressed presidential campaign. You can watch the event live on The Times website, alongside real-time analysis from reporters.

It could prove to be the most crucial 90 minutes of the entire race, our politics reporter Reid Epstein told me. Tens of millions of viewers will tune in for what could be their first unscripted impression of the candidates, just days before early voting begins. Expect Trump to try to shape public perceptions of Harris. And Harris, the candidate many voters say they still need to learn more about, will likely try to define herself on her own terms. Here’s a quick run-down of the debate rules.

Harris, Reid said, “has the opportunity to introduce herself to voters, especially the relatively small subset of those whose votes are up for grabs, and make the case that she is presidential.” Her aides want her to cast herself as a defender of the middle-class and goad Trump — who would be the oldest person ever elected president — into one of his incoherent rants.

Reid added that “Trump, who is much more defined in the public eye, is going to be trying to disqualify Harris by tying her to President Biden.” The former president’s team wants him to turn the conversation back to areas they consider winning terrain: the economy, immigration and global chaos.

Here’s what else to know:

• This is where Harris and Trump stand on key issues, and where they have changed their positions.

• On economic questions, Trump says tariffs are the solution to almost any problem. Harris focuses on reducing prices, a key vulnerability of the Biden administration.

• Trump has vowed to prosecute those he sees as working to deny him a victory.

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