More Americans tuned in to Fox News' Republican primary debate last night than have ever watched a primary debate for either party in history. In fact, the early numbers indicate that viewership may have doubled the previous Republican primary record.

CNN Money sums up Nielsen's initial ratings report: 

The debate on Fox News had a 16.0 household rating between 9 p.m. and 11 p.m., according to Nielsen.

Translation: 16% of United States homes with TV sets tuned in.

Fox News usually has 1% or 2% of the household audience.

For the sake of comparison, the highest-rated Republican primary debates in 2011 and 2012 were watched by approximately 5% of households.

The Democratic primary debates in 2008 were bigger, but none of those ever topped 10%.

The aggressive, relevant, and revealing questions from the debate hosts (Chris Wallace, Megyn Kelly, and Brett Baier) have earned high praise from just about everyone. While frontrunner Donald Trump reportedly had more air time than others, Fox deftly handled the crowded field to allow the American public a chance to hear substantive responses from all ten candidates. As for the true winner of the debate: as the ratings show, clearly it was Fox News. 

Update: It's official: Fox killed it last night, landing 24 million viewers, according to TV Newser, making the debate potentially the "highest non-sports cable program of all time":

A whopping 24 million watched the debate from 9 p.m. ET to just past 11 p.m. ET. FNC drew 7.9 million in the A25-54 demo.

This is poised to be the highest non-sports cable program of all time. It’s already the highest-rated cable news program of all time and Fox News’s most-watched program ever.

Fox's debate also drew massive traffic online (trumping Jon Stewart's farewell Daily Show episode, by the way):

Nielsen Social TV ratings ranked last night’s debate as the number one event on Twitter with 3.3 million tweets and 393 million impressions, beating Jon Stewart’s farewell episode. The debate, which was co-sponsored by Facebook, increased interactions on FNC’s Facebook page by +74 percent from a typical day in July. The 10 million Facebook video views were up +190 percent compared to the daily July 2015 average.