Democratic National Committee Chairman Tom Perez tried to explain why the party will only be featuring white candidates on the debate stage on Tuesday night.

Perez, 58, has been criticized for upholding debate qualification rules that have limited participation from nonwhite candidates. Tuesday night’s debate on CNN will be the first time the debate stage will not feature a single candidate of color.

Speaking with CNN's New Day hours before the debate, Perez was asked to justify the debate standards given the lack of diversity. He explained that the rules had been set and that he would not change them just because the candidates some people wanted to hear from did not make the cut.

“We’ve set a really remarkably inclusive and, frankly, low bar throughout the campaigns, John, and I’m proud of that. And as a result of that, we did have the most diverse field in American history, and I’m proud of that,” Perez said. “And what we said every month was that the closer we got to Iowa, we would do what we’ve always done, which is raise the bar. And last month, we had eight people who made the debate stage: three women, two candidates of color, and an openly gay candidate — remarkable diversity.”

Perez added that he had “no doubt” that Kamala Harris would have qualified for Tuesday night’s debate if she had not dropped out in early December . He added, “She stepped off and suspended her campaign — not because of any criteria that the DNC set but for other reasons. And that saddened me. I take a back seat to no one in my commitment to diversity and inclusion.”

[Related: Cory Booker drops out of 2020 presidential race]

The debate stage on Tuesday night will include six candidates: Joe Biden, Bernie Sanders, Elizabeth Warren, Pete Buttigieg, Tom Steyer, and Amy Klobuchar. Former Vice President Biden, 77, has been the clear front-runner in most nationwide polls but has waffled in Iowa polling as he and Sanders, 78, alter between first and second place. This is the final debate before the Iowa caucuses on Feb. 3.