All five candidates in the first Democratic presidential debate were white. Moderator and CNN anchor Anderson Cooper is white. Anchor Dana Bash, who assisted with moderating, is white.
The only two nonwhite people who participated in the debate were CNN anchor Don Lemon and CNN Español's Juan Carlos Lopez. Lemon didn't even ask questions himself — he introduced video clips from young people. As a result, the majority of screen time occupied by nonwhite people asking questions was on issues that are supposed to be of interest to their particular ethnic groups.
Lemon's first clip introduced a young man (also black) who asked a question about Black Lives Matter. (Late in the debate, Lemon also introduced a young woman who appeared to be white, who asked about climate change and read a question from another woman about cooperating with Republicans.)
Lopez asked a series of questions about allowing unauthorized immigrants to get health care. (In the last half-hour of the debate, he asked a pair of questions about marijuana legalization.)
But by the last half-hour of the debate, the damage was already done. Viewers had noticed that the nonwhite moderators were expected to ask "ethnic" questions first. And since they got so few chances to ask questions at all, those are the ones that stuck.
When you barely include nonwhite moderators, it's easy to tokenize them
Dana Bash got to ask about issues that weren't just "white issues" (though she was tasked with the "women's issues" question of paid family leave). And Anderson Cooper certainly got to ask about issues that weren't just "white issues" or "descended-from-Vanderbilts issues."
In fact, when Cooper challenged Jim Webb on Webb's opposition to affirmative action, he pointed out that "over half" of the Democratic Party is nonwhite. In other words, he acknowledged just how little the debate stage looked like the voters they were supposed to attract.
Lemon and Lopez were the only representatives of that half of the Democratic Party. But they got way less than half the speaking time. They were both supporting players to Cooper. At least Lopez got to ask his own questions, or questions that appeared to be his own; Lemon was tasked with mediating between the candidates and the questions of "young people." (Of course, the fact that the only "young person" who was visibly nonwhite was the one who asked about Black Lives Matter raises its own questions about what issues CNN thinks are important to young people.)
So it's not surprising that even though both Lemon and Lopez weren't just limited to "ethnic" questions, the debate gave the impression that that was their primary role. CNN apparently wanted to be sure to address issues it thought were particularly relevant to black and Latino voters, and to have black and Latino people do it. But CNN simply didn't give black and Latino people many chances to ask questions, period. So the "ethnic issues" questions were forced to occupy precious slots.
The result isn't exactly tokenization: CNN didn't appear to be bringing in Lemon and Lopez just to address black and Latino issues, respectively. But in its effects, it looks a lot like that. At least some of the CNN debate moderators were aware that the Democratic Party is a lot more diverse than they were. It wouldn't have been that hard to give the nonwhite moderators more time — and with more time, they could have asked more questions that weren't about the issues "people like them" are assumed to care about.