UPDATE: 4:37 p.m. EDT -- The final ratings numbers are in from ratings house Nielsen, and the Fox News GOP debate garnered 12.5 million total viewers, with 3.5 million in the 25-54 demographic that news networks sell to advertisers. Per Nielsen's social media stats, 221,000 people sent more than 1 million tweets over the course of the 2-hour debate, reaching an audience on Twitter of 6.2 million. While this was indeed the second-lowest-rated Republican debate, it did still draw a larger audience than three of the four Democratic primary debates (the first DNC debate, on CNN, had 15.8 million viewers).

Original story:

The early returns are in for the Fox News GOP debate vs. CNN/MSNBC Trump-a-palooza, and the winner is: Fox News, but only by a technical knockout. While Fox News’ debate may have delivered four times the audience as Trump’s charity event, the Republican front-runner’s presence was strongly felt by his rivals, who were forced to answer Trump-related questions on stage at the final debate before next week’s Iowa caucus. In the end, the headline-grabbing Republican Trump managed to be on three channels at once.

Fox News garnered an 8.4 household rating in Nielsen’s metered market overnights, meaning an average of 8.4 percent of households in the 25 biggest markets in the U.S. tuned in. However, that would make this the second-least watched Republican debate out of the bunch. (The lowest-rated was Fox Business Network’s sparring contest two weeks ago.) The biggest debate audience was Fox News’ first outing for the GOP field back in August, with a cable record-shattering 24 million viewers and a 16.0 metered market overnight rating . Thursday’s Fox News debate should come in at around 11 million viewers.

The combined audience for MSNBC's and CNN’s coverage of the Donald Trump charity event/rally only amounted to about 25 percent of the Fox News audience, according to CNN’s Brian Stelter.

The caveat with these kinds of early numbers is that they tend to be directional, and can really only be compared to other programs’ metered market overnights. They also don’t take into account digital streams. Fox News made the debate available to stream for free on its site, and other Republican debates have seen an average of 815,000 streamers.

Trump Republican presidential candidate Donald Trump greets supporters and journalists after speaking at a veteran's rally in Des Moines, Iowa, Jan. 28, 2016. Photo: Reuters/Aaron P. Bernstein

While the candidates who participated won the ratings battle, Trump’s event — in which GOP also-rans like former Arkansas Gov. Mike Huckabee and former Pennsylvania senator Rick Santorum stopped by — ensured Trump was somehow the biggest man in both rooms despite only physically being in one, as the Fox News debate saw quite a few references (oblique or otherwise) to the front-runner.

The Iowa caucus starts on Monday. Trump is leading in all polls in Iowa and nationally, followed by Ted Cruz.