Brady Quirk-Garvan, who spent the past five years as the head of the Charleston Democratic Party before endorsing Booker this month, said Sanders’s ­behind-the-lectern style of campaigning had made it hard for him to connect personally with black and poor voters in South Carolina.

“It’s not just that he’s a Yankee. It’s not just that he’s white. It’s not just that he’s old and that he sounds like a professor. It’s all of those things,” Quirk-Garvan said. “When Bernie Sanders speaks, it could be the lecture hall of the Harvard student union. And that’s good and great from a policy standpoint, but that is hard to get people as excited about.”

As for Warren, who actually was a Harvard professor several years ago, after seeing her early campaign events fail to draw many black voters, she has decided to go to them.

She is on a campaign swing this week through the South, touring impoverished neighborhoods in the Mississippi Delta in an echo of the famous “poverty tour” taken by Sen. Robert F. Kennedy (D-N.Y.) in 1967 and 1968. Warren held town hall meetings in Birmingham, Ala., and Memphis, and visited Selma on Tuesday.