And Mayor Eric Garcetti of Los Angeles, who himself mulled a presidential run, endorsed Mr. Biden. The endorsement may help boost Mr. Biden in delegate-rich California, a state that Mr. Sanders is counting on and where former Mayor Michael R. Bloomberg of New York is spending significant resources.

A Steyer surge?

Friday was the deadline to qualify for next week’s debate, and two polls released the day before helped the billionaire former hedge fund executive Tom Steyer slide in at the last minute.

Mr. Steyer had never before exceeded 5 percent in a debate-qualifying poll, but on Thursday, Fox News released polls of voters in Nevada and South Carolina, both states where he has advertised heavily, that found him at 12 percent and 15 percent.

That means the debate stage in Iowa will include six candidates: Mr. Biden, Mr. Sanders, Ms. Warren, Mr. Buttigieg, Senator Amy Klobuchar of Minnesota and Mr. Steyer.

The entrepreneur Andrew Yang is the only candidate who qualified for last month’s debate but not this month’s.

The much-anticipated Iowa Poll, from The Des Moines Register and CNN, was released Friday evening and showed Mr. Sanders in the lead in Iowa for the first time, followed closely by Ms. Warren, Mr. Buttigieg and Mr. Biden. As for Mr. Steyer? He was at just 2 percent.

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