Congressman Gregory Meeks of New York, the chairman of the CBC, tore into Mr. Sanders, a Vermont independent, calling his record on gun control "very troubling" and questioning the significance of his growing roster of black surrogates.

"His record on guns is very troubling. Bernie Sanders voted to protect the gun manufacturers. That's a problem."

Mr. Meeks said Ms. Clinton has been focused on "getting guns off the street" and accused Mr. Sanders, who served in the House for nearly two decades before his election to the Senate, of not being a partner with the CBC. The Queens congressman predicted […] Mr. Sanders […] would fail with the black electorate.

Since both Iowa and New Hampshire are almost entirely white, and Mr. Sanders hails from one of the whitest states in America, the "real primary" is just beginning now, Mr. Meeks argued. He ripped some of Mr. Sanders' most prominent black surrogates, including Dr. Cornel West, a fierce Obama critic. This, along with a focus on Mr. Sanders' gun record, has been an emerging Clinton attack line: that Mr. Sanders, who claims to support President Obama and promises to protect his legacy, aligns himself with the likes of Dr. West, who once called Mr. Obama a "niggerized" president for not challenging white supremacy.

"Cornel West is one of the biggest critics of Barack Obama. People like him don't acknowledge all the good work he's done," Mr. Meeks said. "These are all critics of Barack Obama, which means Sanders is a big critic of Barack Obama."

Rep. John Lewis, D-Ga., hit Vermont Sen. Bernard Sanders' past activism during the civil rights movement while throwing his support behind former Secretary of State Hillary Clinton for the Democratic presidential nomination.

Lewis was participating in a press conference on Thursday announcing that the Congressional Black Caucus Political Action Committee was endorsing Clinton. In response to a question from Roll Call about Sanders' previous work on civil rights, Lewis, a civil rights leader who chaired the Student Nonviolent Coordinating Committee and spoke at the 1963 March on Washington, said he did not work with Sanders.

Lewis' remarks contrast with Sanders' frequent highlighting of his record on civil rights. Sanders' campaign website bio shows him as an organizer for the Student Nonviolent Coordinating Committee at the University of Chicago to see Martin Luther King — and incidentally, Lewis — speak in 1963.