WESTERVILLE, Ohio — The Democratic debate stage is getting bigger, but television ratings are getting smaller.

The primary debate on Tuesday night in Ohio, co-sponsored by CNN and The New York Times, drew about 8.3 million live television viewers on CNN, Nielsen said on Wednesday. The event featured 12 candidates, up from the 10 who debated last month in Houston at an event seen by about 14 million people on ABC News and Univision.

Interest in the 2020 presidential race is clearly strong. The 8.3 million people who watched on Tuesday roughly equaled the number of viewers for a 2008 matchup between Barack Obama and Hillary Clinton, days before the so-called Super Tuesday primary night.

But the three-hour Ohio event — which featured a cavalcade of candidates attacking Senator Elizabeth Warren of Massachusetts — did not perform much better than this year’s lowest-rated primary debate, a CNN forum in late July in Detroit with 8.2 million viewers.