In June and July, Fox News was the highest-rated television channel in the prime-time hours of 8 to 11 p.m. Not just on cable. Not just among news networks. All of television. The average live Fox News viewership in those hours outstripped cable rivals like CNN, MSNBC and ESPN, as well as the broadcast networks ABC, CBS and NBC, according to Nielsen.

That three-hour slot is a narrow but significant slice of TV real estate, and it is exceedingly rare for a basic-cable channel to outrank the Big Three broadcasters, which are available in more households and offer a wider variety of programming.

Even the return of live sports did little to stop the momentum: The Fox News programs hosted by Mr. Carlson and Sean Hannity drew more live viewers than competing baseball and basketball games, including a Yankees-Nationals matchup on Opening Day.