(WASHINGTON) — Renewed concerns about dwindling diversity in the presidential field are brewing among some Democrats after Julián Castro, the lone Latino candidate running, announced the suspension of his campaign Thursday. In a video message released on Twitter, the former Obama administration Housing and Urban Development secretary expressed his gratitude to all of his supporters who supported his “bold vision” for the country, opting to focus on a romanticized version of his campaign story, rather than the uphill battle he has faced since he entered the race last January. In recent months, his campaign struggled to compete with opponents with higher name recognition, massive fundraising efforts, or virtually unlimited campaign funds. Castro eventually failed to meet polling and fundraising thresholds which prevented him from participating in the November and December Democratic debates. Castro, the first Mexican-American to have sought the presidency, had used his campaign as a platform to champion issues affecting communities of color and immigrants, pushing progressive policy proposals such as the decriminalization of border crossings, reparations for the descendants of African-American slaves and calling for the legalization of marijuana.His departure from the race comes less than a month after Sen. Kamala Harris, D-Calif, one of only two female candidates of color, stunned political circles with the sudden suspension of her presidential bid after fielding criticisms of a disorganized campaign operation, a plateau in polling and a dried up campaign bank account. Within hours of Castro’s announcement that he was leaving the race, Sen. Cory Booker, D-NJ, one of two African-American Democratic presidential candidates left in the race, sent a fundraising email to supporters titled “Julián Castro.” In the email, Booker suggests billionaire candidates with “bottomless checkbooks” had pushed out yet another candidate of color. “Julián’s early exit is a loss for our party and this nominating process,” Booker says in the fundraising email. “We need Cory’s voice now more than ever.”Out of 14 Democrats still standing, only four identify themselves as candidates of color. Rep. Tulsi Gabbard, D-Hawaii, is of Southeast Asian, Polynesian and Caucasian descent, former Massachusetts Gov. Deval Patrick is African American as is Booker and businessman Andrew Yang is Asian American. “Minority outreach has to be sincere, it has to be sustained,” says Matt Barreto, professor of political science and Chicano Studies at the University of California, Los Angeles. “It has to be integrated into their campaign at senior levels, not just window dressing.” Experts say Castro’s biggest roadblock may have been the same issue Harris faced; questions of electability against President Donald Trump. “Nominating someone who can beat Donald Trump has become more important, given this divisive climate,” explains Melissa Michelson, Menlo College political science professor, and president of the American Political Science Association Latino Caucus.In a recent Quinnipiac University national poll released last month, former Vice President Joe Biden dominated the field when Democratic voters and independent voters who lean Democratic were asked how likely it is that each of the top Democratic candidates would win against President Donald Trump in the 2020 presidential election. Biden led with 44% of the vote, trailed by Sen. Bernie Sanders, I-Vt., at 15%, Sen. Elizabeth Warren, D-Mass., with 9%, and former New York City Mayor Michael Bloomberg at 7%. All other candidates, including Castro, polled at 3% or below. In the poll, 54% of black respondents said they believed Biden had the best chance of defeating Trump in 2020, followed by Sanders at 10% and Warren with 6%. Quinnipiac’s poll did not further break down data pertaining to other minority voters, only categorizing voters as black or white. As recently as late December, Castro was lamenting about the lack of diversity on the upcoming January debate stage set to take place in Des Moines. Castro suggested the Democratic party nominating process was giving a leg up to candidates who prioritized Midwestern voters. He went on to say winning in 2020 meant also showing the diversity of the Democratic party.Although Castro highlighted his background often while campaigning, in several instances, he said he did not think people should vote for him solely because of his ethnicity. “I don’t want anybody to vote for me just because of the color of my skin or to vote against me,” Castro told reporters during a call about his fundraising efforts following the departure of Sen. Kamala Harris from the Democratic primary in early December. “I do believe though, that whether voters see a diverse field of candidates being able to present their case, that makes a difference.” Although Castro used the lack of diversity in the race as a way to capitalize on fundraising efforts for his campaign, he was often critical of the media for grouping all minority candidates into one category, rather than treating them as individuals with distinct personal backgrounds and histories.“Candidates of color have different backgrounds and history, so we can’t lump everybody together,” Castro said in the late December MSNBC interview. He detailed the criticism he faced when he first launched his campaign for not speaking fluent Spanish. Castro also faced criticism from fellow Democrats when he became the first Democratic presidential candidate to introduce a comprehensive immigration plan to support making crossing the border illegally a civil rather than criminal offense. His narrative on immigration thus became a centerpiece for his campaign and went on to help influence the plans of many of his fellow candidates. “It’s devastating,” explains Michael Jeffries, an associate professor and chairman of American Studies at Wellesley College, regarding the effect of Castro’s exit on the discussion of immigration reform. “Not only because Castro has the best understanding of the current immigration crisis, but also because he is the most skilled communicator on this issue. Immigration has to be a priority for the Democrats for political and moral reasons, and the remaining candidates would be wise to seek Castro’s help as they reframe the debate and make the case for immediate reform,” Jeffries said. The question of Castro’s next steps remain uncertain. He ended his final campaign video Thursday with the words “ganaremos un dia” translated from Spanish to mean “one day, we will win,” a potential foreshadowing of the secretary’s future political prospects. Some politicos have suggested he could be on the several candidates’ short list for vice president. Liz Mair, a Republican strategist, posited in a New York Times op-ed published Thursday, that Castro would be a “valuable” asset to any Democratic ticket, because of “zero-damns-given attitude” and his “lack of interest in deferring to the supposed power players, the bright and shining stars, the elders in the room.” It would not be the first time Castro’s name was floated as a possible vice presidential pick. He was shortlisted and vetted as a vice-presidential candidate during former Secretary of State Hillary Clinton’s 2016 presidential campaign. Clinton eventually chose Virginia Sen. Tim Kaine with Castro campaigning for Clinton as a surrogate. However, in a February interview on Jimmy Kimmel Live!, Castro said he would not be interested in the vice-presidency, telling Jimmy Kimmel, “No, no, I’ve been there and done that last time.” Copyright © 2020, ABC Audio. All rights reserved.