The Democratic presidential candidates smashed a ratings record on Wednesday night, drawing a combined audience of 19.7 million to the latest primary debate, Nielsen said on Thursday.
Shown on NBC and MSNBC from the Paris Theater in Las Vegas, the broadcast was the most watched in the history of Democratic presidential primary debates. It beat the previous record-holder from June, when 18.1 million viewers tuned in to NBC, MSNBC and Telemundo for the second Democratic debate of the current election cycle.
Before the Wednesday debate, viewers’ interest in the Democratic matchups had seemed to level off. Since October, an average of roughly six million to eight million people tuned in for the last five contests, according to the Nielsen ratings.
For some context: Last night’s viewership totals across the two networks outperformed two other live prime-time events this year, the Grammy Awards (18.7 million viewers on CBS) and the Golden Globes (18.3 million on NBC).
The Wednesday debate may have generated interest thanks to the addition of a newcomer: Michael R. Bloomberg, the former New York City mayor, who has spent hundreds of millions of dollars on television commercials and online ads since entering the race in November.
Mr. Bloomberg is not on the ballot for the next contest — Saturday’s Nevada caucuses — but rival television executives signaled before Wednesday’s debate that viewer interest would be stoked by the prospect of watching the billionaire mix it up with five Democratic rivals.
Mr. Bloomberg seemed sluggish as he tried to fend off frequent attacks from his competitors, most notably by Senator Elizabeth Warren. Nearly eight months after the current cycle’s first Democratic presidential debate, the Las Vegas edition was the most energetic, freewheeling and ferocious so far.
The moderators were Lester Holt and Chuck Todd of NBC, Hallie Jackson of NBC and MSNBC, Vanessa Hauc of Noticias Telemundo and Jon Ralston of The Nevada Independent. Ms. Hauc had a tense face-off with Senator Amy Klobuchar after pressing her on her failure to name the president of Mexico during an interview on Telemundo this week.
The great majority of viewers did not turn away as the two-hour debate went on. In the first hour, which started at 9 p.m. Eastern time, the average combined audience for NBC and MSNBC stood at 19.9 million. In the second hour, 19.4 million were watching, according to Nielsen.
The debate took place at a critical juncture of primary season: After voters in Iowa and New Hampshire had winnowed the field, but before key contests in Nevada, South Carolina and Super Tuesday states.
The first Republican debate from August 2015 — Donald J. Trump’s debut on the debate stage — remains the most watched of primary debates. That broadcast, on Fox News, drew 24 million viewers.
Viewers will not have to wait long for the next episode. CBS is scheduled to broadcast a debate on Tuesday from South Carolina. The moderators will be led by the “CBS Evening News” anchor Norah O’Donnell and the “CBS This Morning” co-host Gayle King.