Washington (CNN) Democratic National Committee chairman Tom Perez on Tuesday defended the party's primary debate qualifications and nominating process amid accusations that the party is lacking diversity amid its top 2020 contenders.

But in an interview with CNN's John Berman on "New Day," Perez said the party cannot change its rules to ensure minority candidates don't drop out before the nominating process begins, a day after one of the field's most prominent black candidates suspended his campaign after not qualifying for the debate.

"We've set a really remarkably inclusive, and frankly low bar throughout the campaigns ... and I'm proud of that," Perez said. "And as a result of that, we did have the most diverse field in American history. And what we've said every month was that the closer we got to Iowa we would do what we've always done, which is raise the bar."

He continued: "But we made the rules, they were very transparent, they're very inclusive, and we can't change the rules midstream because there's a candidate that I wish were on but didn't make the debate stage."

Later Tuesday, six Democratic candidates will participate in a CNN/Des Moines Register Democratic debate in Iowa, the final debate before the state holds its caucuses next month. In order to qualify for the debate, candidates needed to meet polling and fundraising minimums, the DNC has raised since the previous debate in December.

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