Washington(CNN) To New Jersey Sen. Cory Booker and former Secretary Julián Castro, Sen. Kamala Harris' exit from the 2020 presidential race is a gut check moment for the Democratic Party.
The two Democrats are seizing on Harris -- the only black woman running for president -- dropping out of the race to raise the question about what the prospect of this month's Democratic debate featuring only white candidates could mean for a party the not only prizes diversity, but relies on black voters.
For the candidates, the push is both practical and political.
Both are a long way from qualifying for the December Democratic debate, so looking for attention around the lack of diversity atop the Democratic field makes tactical sense. The duo are also markedly cash-strapped, so fundraising off Harris' exit is not only sensible, it's necessary.
Beyond that, though, Castro, who is Latino, and Booker, who is black, are asking a deeper political question about the party as the December debate currently only features former Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren, Vermont Sen. Bernie Sanders, South Bend, Indiana, Mayor Pete Buttigieg, Minnesota Sen. Amy Klobuchar and businessman Tom Steyer -- all of whom are white.
(Both businessman Andrew Yang, who is Asian, and Hawaii Rep. Tulsi Gabbard, who is Asian and Pacific Islander, are one poll away from qualifying for the contest in Los Angeles.)
Booker has expressed deep frustration -- even anger -- at Harris' departure, noting with concern that there are now "more billionaires than black people" in the race for president, a talking point aimed at his Democratic rivals Bloomberg and businessman Tom Steyer.
"What message is that sending, that we heralded the most diverse field in our history, and now we're seeing people like [Harris] dropping out of this campaign?" Booker said Thursday in Iowa, as he kicked off a swing through the state.
"This is not about one candidate," he added. "It is about the diverse coalition that is necessary to beat Donald Trump."
Likewise, Castro has expressed astonishment that a late-in-the-process Democratic debate could feature only white candidates, using it to question the process that the Democratic National Committee has used to ensure the debate did not include every candidate running.
"What we're staring at is a DNC debate stage with no people of color on it," Castro told reporters this week. "That does not reflect the diversity of our party or our country. We need to do better than that."
The debate over diversity is a complicated one for top Democratic operatives and the Democratic National Committee. Most operatives agree that the party needs to set standards on who makes the debate stage as a way to allow the candidates getting the most support to get the most time on the debate stage.
But there is also widespread acknowledgement that the party needs to showcase its diversity, especially considering black voters make up the backbone of the party. In 2016, for example, black and Latino voters made up 23% of the electorate, with 89% of black voters and 66% of Latinos backing Hillary Clinton over Donald Trump.
"If the December debate stage is all white, mostly older, and mostly male, the Democratic Party has a serious crisis on its hands," said Jess Morales Rocketto, a Democratic operative who recently worked for the National Domestic Workers Alliance.
"After we presented a historic field, the cracks in the primary system have presented themselves at every turn -- money doesn't equal enthusiasm, polls don't sample enough voters of color, not enough pundits understand cultural context of their candidacy," said Rocketto. "Why can candidates of color can only garner support when they are in danger of being on stage at all?"
The DNC said in a statement that the process has been its most inclusive.
"This has been the most inclusive debate process with more women and candidates of color participating in more debates than billionaires," DNC spokeswoman Xochitl Hinojosa told CNN in a statement. "We are proud of this historic and diverse field with 20 candidates participating in the first two debates and at least 10 candidates in each debate after that. While we are legally required to have objective criteria for each debate, our qualifying criteria has stayed extremely low throughout this entire process. Nobody who has failed to reach 4% at this point in the race has gone on to be the nominee, and our debate criteria reflects that. In addition, we have made diversity a priority by requiring that every debate have women and people of color as moderators. We've never seen a political party take this many steps to be inclusive."
Booker and Castro have been sounding the alarm for months now on the need for Democrats to focus on building and exciting such a coalition.
Castro, as he struggled to gain attention in Iowa and New Hampshire, slammed the party for allowing two predominantly white states -- Iowa and New Hampshire -- to be the first to vote in the process.
"We need to change the whole game, there is no reason that Iowa and New Hampshire should go first, two states that hardly have any black people in them," Castro said in California on Thursday.
Booker, during a July speech at the National Urban League Conference in Indianapolis, also warned that Democrats concerned about electability should not focus solely on winning back the white working class voters who defected in 2016 to support Trump — but must also nominate a candidate who could energize African Americans who did not vote in 2016, a fact that contributed to Clinton's surprising shortfall in key Midwestern states.
After Harris' shock decision to end her campaign, however, Booker's team believes Democrats might now begin to heed his warning.
"To see such a qualified black woman not even end up as one of the choices on the ballot is a moment that I think is leading to some introspection about where we are in this primary and what we need to win next November," Booker's campaign manager Addisu Demissie said.
It's not just about waking up complacent voters, Booker's team believes, but also reorienting the thinking of a Democratic Party that has heaped its focus on appealing to moderate white voters, more so than turning out black voters who were at the core of the winning Obama coalition.
"There's an education that needs to be done with voters and donors and reporters alike on that," Demissie said, "and that's part of what a campaign is."
Both Castro's and Booker's campaigns have said they have seen a rush of support in the wake of Harris getting out, something they attribute to voters wanting to see diverse options on the stage.
A Castro aide said Thursday that they have raised more than $200,000 since Harris dropped out, one of the biggest surges Castro has had since failing to qualify for the November debate.
For Booker, Wednesday -- the day after Harris got out -- marked his biggest day of online fundraising to date, an aide said. All told, 11,000 new donors have contributed to Booker's campaign since Harris dropped out.
The moment might be coming too late for both, however.
With zero of four qualifying polls needed to earn a spot in the December debate, Booker and Castro are likely to be excluded from the stage. This is the first time Booker won't qualify for a debate and it's unclear what will happen for his campaign after that.
To Karen Finney, a senior aide to Clinton's 2016 campaign and senior adviser to Georgia gubernatorial candidate Stacey Abrams in 2018, Harris' getting out and the lack of diversity atop the field is a "gut check moment" for the party and could impact the party for years to come.
"What sets this cycle apart from others is the strong desire among Democratic base voters to beat Donald Trump," Finney said. "And yet, time and again, (voters) continue to say that a white man may be the best person to take on Trump; so we all have to check our biases, conscious and unconscious about why that is."
She added: "It also means for voters, especially black and brown voters, those voices and faces are missing from the stage and it sets us back to some degree in sending a message to young people about who can be president, what a leader looks like."