UPDATE 1-Second U.S. Democratic debate sets TV ratings record

About 18.1 million television viewers watched Thursday night's debate among 10 Democrats running for U.S. president, a record for a Democratic primary face-off, according to Nielsen data released by NBC News.

The debate featuring front-runners Joe Biden and Bernie Sanders was shown on broadcaster NBC, cable channel MSNBC and Spanish-language network Telemundo, all owned by Comcast Corp . The previous record for a Democratic debate was 15.8 million viewers, set in October 2015. The biggest primary audience of all time was the 24 million who tuned in for the first performance by Donald Trump in a Republican candidates' debate on Fox News Channel.

During Thursday's event, candidate Kamala Harris dominated her rivals and confronted Biden about his opposition to school busing in the 1970s. The debate was the second of two with Democratic candidates aiming to challenge Trump. An estimated 15.3 million viewers turned in on Wednesday to watch Elizabeth Warren, Beto O'Rourke and eight other challengers, NBC said.