Good Thursday morning, and happy debate day. Here are some of the stories making news in Washington and politics today.

Mr. Biden and Ms. Warren present two starkly different options for Democratic voters, embodying competing theories about what the Democratic Party should stand for and what direction it should take in 2020 .

Join us for live coverage tonight, starting at 8 p.m. Eastern time. Visit NYTimes.com or open the NYTimes app on your smartphone or tablet, then follow along as Lisa Lerer and colleagues chat live during the debate.

The top 10 Democratic presidential candidates will be on a single stage for the first time Thursday night. That means a matchup months in the making — between former Vice President Joseph R. Biden Jr. and Senator Elizabeth Warren of Massachusetts — will come to fruition. Here are other key dynamics to watch for .

Senator Kamala Harris of California had a great June debate, but her campaign lost steam over the summer. Her surrogates, donors, and even some supporters hope that in Houston tonight she can recapture the magic that initially won them over.

In the first debates, Senator Amy Klobuchar of Minnesota refused to embrace the party’s more liberal ideas or draw an explicit contrast with more progressive candidates. It’s a strategy betting on the patience of Democratic primary voters — if only she can attract their attention.