The endorsement by Democratic Rep. Karen Bass of California on Friday is the latest testament of a growing coalescence of support for Biden's White House bid. Biden's campaign has seen a resurgence powered by black voters, who have helped cement his front-runner status after commanding wins in several recent primaries, including in South Carolina, in several Southern states and just this week in Michigan.

"It's very clear to me that he is the best person, not just to beat (President Donald) Trump, but he is the person to lead at this time," Bass said in an interview with The Associated Press. "I think him having a long-standing history of working with African American communities, most notably in his own state but around the country, was qualitatively different from the other candidates."

Biden's progressive rival, Sen. Bernie Sanders of Vermont, who has performed well among younger and Latino voters, has struggled to garner support within the African American community. Black voters will continue to be a key demographic as both campaigns eye upcoming primary contests in states with large black populations, like Georgia.

Bass said she held off endorsing a candidate because two CBC members, Cory Booker and Kamala Harris, were running for president. Booker and Harris have since dropped out and endorsed Biden, a former vice president and U.S. senator from Delaware.

The CBC as a whole is not officially endorsing a candidate, Bass said, but the majority of members have already announced support for Biden. The powerful group, created in 1971, is composed of most African American members of Congress, making up nearly 25% of the Democratic majority in the House. Of the 54-member group, 37 have endorsed Biden, including House Majority Whip Jim Clyburn, who has been credited with helping turn the tide for Biden with a big win in Clyburn's home state of South Carolina.

One member of the CBC, Democratic Rep. Ilhan Omar of Minnesota, has endorsed Sanders.

Although Biden has strong support within the African American community, especially among older voters, concerns have been raised about his ability to energize young and progressive voters.

Bass, a progressive Democrat who is serving her fifth term in a congressional district that includes south Los Angeles and Culver City, said she believes Biden would be able to grow support among those groups, if he were to become the eventual nominee.

"As this race settles down, it is my job personally and the job of members of the Congressional Black Caucus to be extremely clear with people in our districts what is at stake here, and what is at stake is their future," Bass said. "It's a job that we've all been doing over the last 3 1/2 years, but we have to step it up."

Asked whether Sanders and Rep. Tulsi Gabbard of Hawaii should drop out of the race to unite the party before the Democratic National Convention, Bass said she believes the primary process needs to run its course and allow every voter the chance to weigh in.

"I would never be in a position to say, 'You need to drop out,'" Bass said. "I do think, though, that math is math."

She continued: "I think they have to do the soul searching and say, 'Why am I still doing this?' But I think that's an individual decision or a campaign decision."

Bass said she hopes, though, that the eventual nominee considers a person of color as his running mate.

"I think that a presidential candidate has got to choose somebody that they feel that they can trust, that they can work with," Bass said. "Now, having said that, I certainly hope it's a woman. I certainly hope it's a woman of color."