"Black folks are not dumb. They come out for individuals that have their best interest at heart," said New York Rep. Gregory Meeks, chair of the CBC political action committee told CNN's Carol Costello on "Newsroom."
The endorsement's timing was significant, coming just hours before Clinton and Sanders are due to clash in their latest debate in Milwaukee, Wisconsin, in which she is expected to aggressively highlight her record of fighting for African-American voters.
The CBC PAC's backing also bolsters Clinton's effort to position herself as the guardian of the legacy of Barack Obama, the first African-American president, and her strategy of securing the large turnout among black voters she would need in a general election.
"One of the individuals that has been with us time and time again has been Hillary Clinton. She has been, her whole career, an individual that has been fighting for issues that are important to the African-American community," Meeks said.
Rep. John Lewis, D-Georgia, a revered civil rights leader in the 1960s, emphasized that point. He told reporters he didn't recall Sanders' role in the civil rights movement.
"I never saw him. I never met him," Lewis said. "I was chair of the Student Nonviolent Coordinating Committee for three years, from 1963 to 1966. I was involved with the sit-ins, the Freedom Rides, the March on Washington, the march from Selma to Montgomery and directed to voter education project for six years. But I met Hillary Clinton. I met President Clinton."
Thursday's developments are a sign of the increasingly important role of racial politics as the Democratic nominating process as it turns to southern and western states where African-American and Hispanic voters could be decisive.
And it follows a long behind-the-scenes effort by the Clinton family to repair ties to the African-American community which were strained during a sometimes rancorous primary season in 2008 against Obama.
Clinton said she was honored to be backed by the CBC PAC, which comes just two weeks before the South Carolina primary.
"I pledge a new and comprehensive commitment to equity and opportunity for communities of color," she said in a statement.
"That means reforming our criminal justice system and rebuilding the bonds of trust between our communities and our law enforcement officials," she said in a statement. "But it also means making major new investments to create jobs, to make it easier to start and grow a small business, to end redlining in housing, and to build reliable public transit systems."
Sanders is making his own effort to woo African-American voters and opinion leaders. On Wednesday, he sat down with civil rights leader Al Sharpton
, who has yet to endorse and rolled out the backing of Ben Jealous
, the former head of the NAACP.
But he has a significant climb ahead of him. An NBC/Wall Street Journal Marist poll released in late January showed him struggling to attract support among African-American voters in South Carolina, garnering 17% compared to Clinton's 74%.
As he courts African-American voters, Sanders also faces a delicate challenge: He campaigns as a candidate of radical change, which at times means implicitly criticizing Obama's presidency.
In an interview with MSNBC for instance set to air later on Thursday, Sanders knocked Obama for not doing enough to bridge what he said was a "huge gap" between Congress and the American people.
"What presidential leadership is about closing that gap," he told MSNBC in an interview that will air Thursday
evening on "The Last Word with Lawrence O'Donnell."
But his warning could open a lane for a new Clinton attack.
The former secretary of state's campaign responded to Sanders by tweeting an article about his comments and parodying the soundbite that got Republican candidate Marco Rubio
into trouble in last week's GOP debate.
"Let's dispel with this fiction that @POTUS doesn't know what he's doing. He knows exactly what he's doing," the tweet said, striking a theme that Clinton could use in the debate to portray herself as the heir to Obama, who remains highly popular among African-American Democrats.
Key community leaders at the CBC PAC rollout event at the headquarters of the Democratic National Committee in Washington also questioned the commitment of Sanders to the history of the African American community.
North Carolina Rep. G. K. Butterfield sought to distinguish Clinton from Sanders as a candidate with foreign policy experience, achievable goals and an awareness of issues affecting African-Americans.
"We must have a president who is knowledgeable on both domestic and foreign policy," said Butterfield, chairman of the Congressional Black Caucus. "We must have a president who understands the racial divide, not someone who just acquired the knowledge recently."
"We need a president who doesn't simply campaign and promise wonderful things -- things that are politically impossible to achieve," he added.
House Minority Leader Nancy Pelosi called the CBC PAC endorsement "a very big deal" but stopped short of endorsing Clinton herself during her weekly news conference.
Meanwhile Sanders' backer backer and CBC member Keith Ellison made clear that though the CBC PAC had endorsed Sanders, the CBC itself had no input into the decision.
"Cong'l Black Caucus (CBC) has NOT endorsed in presidential. Separate CBCPAC endorsed withOUT input from CBC membership, including me."
Clinton received support from 90% of the CBC's political action committee in the vote by the board, and Sanders did not receive any votes. Ellison, however, does not sit on the board and therefore did not get a vote.