The new survey shows Biden now favored by 29 percent of registered voters who are Democrats or Democratic-leaning independents. Sanders runs next with 19 percent, followed by Warren at 18 percent. In July, Biden was at 30 percent, Sanders at 19 percent and Warren at 12 percent among Democratic-leaning voters.

Only six other candidates register at 2 percent or more. Harris has 7 percent support, down from 13 percent after the first debate. South Bend, Ind., Mayor Pete Buttigieg is supported by 4 percent, former congressman Beto O’Rourke (D-Tex.) and entrepreneur Andrew Yang by 3 percent apiece, and Sen. Amy Klobuchar (D-Minn.) and Rep. Tulsi Gabbard (D-Hawaii) by 2 percent of Democratic-leaning voters each.

Biden has put significant stock in his poll standing, using an early television ad in Iowa to tout his advantage over Trump in general-election matchups. During a conference call with reporters last week, Biden advisers said his advantage in Democratic primary polls represents far more than simply name identification and is based on voter knowledge of his years in the Senate and as President Barack Obama’s vice president.