The ratings, though down from NBC’s set of Democratic debates in late June, reflect ample interest in the sprawling field of candidates that want to challenge President Trump.
The two-hour debate out-rated “America’s Got Talent” on NBC, which averaged 7.9 million TV viewers, and the season finale of “The Bachelorette” on ABC, which averaged 7.4 million.
CNN expected stiff ratings competition from those two reality shows.
Among people watching at home via traditional TV, the debate averaged a total of 8.7 million viewers across CNN and its Spanish language channel CNN en Español.
The first night of last month’s two-night debate averaged 15.3 million viewers, but those face-offs were televised across two broadcast networks (NBC and Telemundo) and the cable channel MSNBC.
NBC also had the advantage of going first. In the run-up to the 2016 election, the first Democratic and Republican debates of the cycle were the most-watched for each party.
The cycle’s first Democratic debate, held in October 2015 on CNN, averaged 15.4 million viewers.
The second Democratic debate, held one month later on CBS, averaged 8.5 million viewers — about in line with Tuesday night’s ratings for the second debate of this cycle.
The Democrats have not come close to generating the kind of viewership interest that the Republicans did in the run-up to 2016.
The first GOP debate of the season, held in August 2015 on Fox News, scored 24 million viewers. The second debate, held one month later on CNN, averaged 23 million.
All of these viewership numbers are from Nielsen, which counts people watching at home on TV sets in the United States. Out of home viewership is measured separately.
CNN also live-streamed the debate on its websites and apps. The company said 516,000 people live-streamed each minute of the debate on average, which is equivalent to the way TV ratings are estimated, adding about half a million to the overall total audience.
Streaming viewership peaked in the second hour of the debate, at 9:35 p.m. ET, when 708,000 people were watching online at the same time. CNN said this streaming viewership ranks “in the top 10 of all events for 2018/2019.”
Other big event days included midterm election night and Robert Mueller’s testimony last week. Overall CNN said there were 2.8 million live video starts on its websites, mobile apps and streaming platforms.
The second night of CNN’s debate, on Wednesday, will feature former Vice President Joe Biden and Sen. Kamala Harris at center stage along with eight other contenders.