At 11:30 a.m. on Saturday, Americans all over the country began flicking on their TVs.
Moments after CNN and most of the major television networks declared that Joseph R. Biden Jr. had defeated President Trump in the presidential election, viewership surged across the three major cable news networks and the Big Three broadcast networks, according to Nielsen Media Research.
On CNN, viewership jumped 36 percent at 11:30, six minutes after the network became the first to project the Biden win. The MSNBC audience jumped 29 percent at 11:30. (NBC News had made its call at 11:25.) On Fox News, which made the call at 11:40, there was a 38 percent jump. The broadcast networks broke into “special report” mode and also saw huge spikes, according to Nielsen.
In all, more than 21 million viewers across the six networks took in the news that Mr. Biden would be the 46th president, an unusually high total for a weekend morning.
CNN had, by far, the most viewers of any network, averaging around seven million between noon and 2 p.m. Eastern time. MSNBC, the home network for many liberal viewers during the Trump years, had an average of roughly 4.5 million. Fox News, which usually has a commanding lead in viewership, had about three million.
Fox News viewers also began to tune out a little more quickly than viewers of the other cable networks, not long after being greeted to gleaming graphics that Mr. Biden was now president-elect. Viewers started to leave Fox News around noon, about 20 minutes after the network made its call, according to data from Nielsen.
By 3 p.m., as cable viewers began to tire of the roundtable discussions about a Biden presidency, CNN had lost 24 percent of its noon audience and MSNBC 23 percent. But Fox News had shed 45 percent of its audience, to about 1.8 million viewers from about 3.4 million at noon.
The gap between Fox News and other networks was even more pronounced Saturday night. More than 35 million watched Mr. Biden and Vice President-elect Kamala Harris’s prime-time speeches, according to Nielsen. CNN commanded the largest audience, with 13.6 million, and MSNBC had the second-highest total, 8.5 million. CBS led the broadcast networks with 5.6 million.
But Fox News had the smallest viewership of any network that carried the speech: Only three million watched.
No television executive anticipated that this trend would last longer than a day or two. Fox News has hit record ratings marks throughout the year. It scored the highest viewership in prime time on election night of any network.
And indeed, by Monday, it appeared that order had been restored. Fox News won in prime time as its hosts Tucker Carlson, Sean Hannity and Laura Ingraham — who continued to discuss the Trump campaign’s baseless claims about voter fraud and other alleged election irregularities — averaged 3.8 million viewers, a million better than MSNBC and 1.3 million better than CNN.