In this debate, Senator Elizabeth Warren is at the top, as the only candidate polling in the double digits, followed by Senator Cory Booker, who is running a campaign of “love,” and Beto O’Rourke, who has expertise on immigration and President Trump’s border wall proposal. Here are some of the other story lines and political dynamics to watch for.

Wax poetic: A comedy writer roasted all the Democratic candidates by haiku in an Opinion piece for The Times.

The details: NBC, MSNBC and Telemundo (in Spanish) will show the debate on network TV and on their streaming platforms. Here’s a look at possible questions.

The Daily: In our latest episode, a Times political reporter discusses what’s at stake .

Separately: Robert Mueller, the former special counsel, is scheduled to publicly discuss his investigation — a topic that hangs over the 2020 race — during two hearings in Congress next month.

A new potential flash point in Iran crisis

Iran, responding to American sanctions, has said that by Thursday its uranium stockpile will have exceeded the limits set in the 2015 agreement that President Trump pulled out of last year.

This milestone would come amid increasing tensions between Iran and the U.S. and could thrust the crisis into a combustible new phase.