Besides, even during his early 2010 heyday, Fox was unable to generate advertising revenues to match Mr. Beck’s ratings, since no reputable company would sign on to sponsor the guy who accused Mr. Obama of harbouring a “deep-seated hatred for white people.”

Mr. Beck’s ratings plummeted 31 per cent in the first three months of 2011, compared with the same period last year. His audience among viewers in the key 25-to-54-year-old cohort plunged 38 per cent to fewer than 500,000.

Mr. Beck has still been drawing almost two million viewers during his 5 p.m. time slot, which is more than the number who tune in to the four competing cable news channels combined. But Beck diehards tend to be older, while serious political news junkies are returning again to CNN.

For months, reports have been surfacing about a souring of the relationship between Mr. Beck and Fox president Roger Ailes. Notwithstanding its “Fair & Balanced” tagline, the network owned by Australian magnate Rupert Murdoch is an unapologetic champion of the right. But Mr. Beck’s bombastic, and regularly offensive, commentary had become a drag on the Fox brand.