New York (CNN Business) An average of nearly 20 million viewers tuned into Wednesday night's Democratic primary debate hosted by NBC in Las Vegas, making it the most-watched Democratic primary debate of all time, according to preliminary numbers.

The early figures from Nielsen Media Research, a firm that measures the size of television audiences, indicated that approximately 19.7 million people on average watched the debate on NBC and MSNBC combined.

Until Wednesday night, the most-watched Democratic primary debate ever had been one that occurred in June 2019, when approximately 18.1 million combined viewers watched the second night of a two-part debate series on NBC, MSNBC, and Telemundo.

The most-watched primary debate of all time still belongs to the 2015 Republican presidential debate in Ohio, for which approximately 24 million people tuned into Fox News. That debate was the first of the 2016 Republican GOP primaries, and featured then-candidate Donald Trump on the debate stage for the first time ever.

The dramatic rise seen in ratings for Wednesday night's Democratic debate came as the stakes for the winnowed down field of candidates increased.

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