DETROIT — As CNN executives prepare for the second night of their debate extravaganza here, they received some underwhelming news: The first night’s proceedings, featuring some masterful comments from Sen. Elizabeth Warren (D-Mass.), drew 8.69 million viewers, according to numbers from Nielsen’s fast national ratings.

That’s a steep drop in viewership compared with the two debate nights hosted by NBC News in Miami in June. Those events drew 15.26 million and 18.1 million viewers, respectively, with that second figure establishing a record audience for a Democratic primary debate. (The all-time primary debate record is Fox News’s Donald Trump-infested smackdown in August 2015, with more than 24 million viewers.) There’s a significant asterisk to the comparison, however, in that CNN’s numbers from Tuesday night stem from CNN and CNN en Español; the NBC audience stemmed from NBC, MSNBC and Telemundo — giving CNN’s competitor a significant advantage in the number of platforms.

CNN sustained criticism online for a long preamble to last night’s back-and-forth with 10 Democratic candidates. That said, it provided a full two hours of bona fide debate. Throughout the night, the moderators — Jake Tapper, Dana Bash and Don Lemon — persistently asked the participants to answer criticism leveled by their peers over the course of the campaign. It was a fire-starter scheme designed to get the candidates to articulate what was unique about their approaches. This moderation tack, too, caught some flak, with one critic describing it as “cyclical, and cynical." Not to mention educational: The small-bore disagreements among the Democratic field need to be highlighted at some point or another. Who’s got a better idea?

The divide-and-highlight approach surfaced a number of illuminating policy discussions that may not have fascinated the average TV watcher. It’s unclear how much nitty-gritty health-care chatter the country will sit for. Accordingly, the audience for these debates may plateau or even drop off, as happened between the first two Democratic debates during the 2016 presidential election cycle.

For CNN’s record books, Tuesday night’s debate was its second-highest-watched contest, behind the Las Vegas Democratic debate that it hosted in October 2015 (15.46 million viewers). There are many reasons why CNN wants big ratings — money, job security for executives, bragging rights — but a key consideration is the Democratic National Committee, which partners with news organizations for these events. In June, after the first night’s ratings numbers came out, DNC Chairman Tom Perez told the Erik Wemple Blog, "We wanted to maximize eyeballs. The more people that watch our candidates, the more people are going to like our candidates.”

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