Former South Bend, Indiana, Mayor Pete Buttigieg’s presidential campaign filled less than half of the delegate slots for the four most diverse congressional districts in Illinois, a sign of how his campaign continues to struggle with Black and Latino voters.

Voters in Illinois cast ballots not only for their pick for president, but also for delegates to the Democratic National Convention. Delegates are generally associated with one of the presidential campaigns, meaning each campaign needs to find 101 people willing to serve as a delegate — at least three in each of the state’s 18 congressional districts, with additional delegates in more heavily Democratic districts.

Finding a person to fill each slot — and collecting the 500 signatures necessary to put them on the ballot — is considered an early test of a campaign’s strength in the delegate-rich state, and supporters of Buttigieg’s rivals said his failure to fill the slots points to a potentially fatal weakness with voters of color.

The three leading Democratic candidates in national polling all filled an overwhelming majority of slots. Massachusetts Sen. Elizabeth Warren and Vermont Sen. Bernie Sanders filled every available slot, while former Vice President Joe Biden filled all but three slots. Buttigieg, who trails the other three candidates in national polling but is a top contender in the early voting state of Iowa, filled just 53 of the slots. Two lower-profile candidates, Minnesota Sen. Amy Klobuchar and entrepreneur Andrew Yang, both filled more than 60 slots.

Buttigieg’s missing delegates are concentrated in the state’s most diverse congressional districts, according to an analysis of candidate data files from the Illinois State Board of Elections. Illinois has two majority-Black districts: The 1st, represented by Rep. Bobby Rush, and the 2nd, represented by Rep. Robin Kelly. Buttigieg filled zero of the eight slots in the 1st District, and just four of seven slots in the 2nd District.

Randall Hill / Reuters Former South Bend, Indiana, Mayor Pete Buttigieg campaigns in South Carolina, a state where polls show him struggling with African-American voters.

In the 7th District, which is plurality Black and represented by Rep. Danny Davis, Buttigieg filled six of eight slots. (Of the four delegates in the 7th District, the Buttigieg campaign said two are Black and two are Hispanic.)

The state also has a lone majority-Hispanic district, the 4th, which is represented by Rep. Chuy Garcia. Buttigieg filled just a single delegate slot of the five available there.

Buttigieg’s campaign said they selected 109 people to run for slate positions, some of whom failed to collect the signatures necessary to make the ballot. Of those 109, the Buttigieg campaign said, half are women, one-fifth are Black, 15% are Latino, 18% are LGBT and nearly a third are under 30.

“We are proud of our volunteers’ hard work to collect more than 6,000 signatures and put Pete on the ballot to ensure he is eligible to earn the maximum number of delegates in every congressional district in Illinois,” Buttigieg spokesman Sean Savett said. “The delegate petitioning process is onerous and complex, especially for those new to the political process. We’re glad we’re bringing in so many fresh faces who have never run for delegate before or been to a convention. Our campaign will have a diverse slate of delegates on the ballot in March, and we will continue to build a group of Illinoisans to serve as delegates for Pete that is reflective of the diversity of our country.”

Buttigieg’s failure to get delegates on the ballot in majority-minority parts of a state where his campaign is partially headquartered is likely to generate further questions about his ability to attract enough support from Black and Latino voters to win the nomination ― and if he has the ability to motivate enough turnout from voters of color to defeat President Donald Trump in November.

“No Democrat wins the White House without significant support from the Black community, the Latino community and young people,” said Chicago Alderman Carlos Ramirez-Rosa, a Sanders supporter. “I just don’t see his campaign connecting with Black and Latino communities, and I’m not sure he knows how to connect. It means he would have a very difficult time beating Trump.”

Buttigieg does have some support from minority communities in Illinois: State Rep. Lamont Robinson, the first openly gay Black man to serve in the state legislature there, endorsed him in September.

Finding sufficient delegates in Illinois and placing them on the ballot is a famously labor-intensive process for presidential candidates of both parties. Ultimately, candidates pay little electoral price for failing to do so: If a candidate receives 15% of the vote in a given district, the state Democratic party will assign delegates to them after the primary. The campaigns of former New York City Mayor Michael Bloomberg and businessman Tom Steyer, for instance, did not field any delegates.

Illinois’ primary is late: It will be on St. Patrick’s Day, two weeks after an overwhelming number of delegates are awarded on Super Tuesday. But as a heavily Democratic and heavily populated state, its 155 delegates could prove crucial in a close race.

Buttigieg’s struggles with voters of color are well-documented, and date back to his earliest days as mayor. In a CNN poll conducted in mid-December, for instance, 8% of Democrats nationally said they planned on backing Buttigieg in the primary, but only 2% of nonwhite Democrats did. A late November poll from Victory Research, however, did find stronger support for Buttigieg among voters of color in Illinois.

Buttigieg is not the only candidate in the sprawling 2020 Democratic presidential field who has struggled with ballot qualification. Yang failed to make the ballot in Ohio because of a bureaucratic error by his campaign, and his supporters have now launched a write-in effort, Biden is reportedly struggling to make the ballot in Indiana, and former Massachusetts Gov. Deval Patrick failed to collect enough signatures for the ballot in Michigan.