Gary Levin

USA TODAY

The forced exit of Fox News Channel's top-rated star will surely have an impact on cable's No. 1 network. Just how much — and how soon — is unclear.

Bill O'Reilly, the subject of multiple accusations of sexual harassment dating back years, was summarily dropped Wednesday by parent 21st Century Fox, amid mounting protests, an advertiser boycott of his O'Reilly Factor, staff unrest and new charges from other women. His expected April 24 return from a planned vacation — he was photographed visiting the Pope at the Vatican on Wednesday — won't happen.

Instead, Fox News announced, Tucker Carlson Tonight will move an hour earlier beginning Monday , replacing The O'Reilly Factor at 8 ET/PT, while a late-afternoon roundtable show, The Five, will replace Carlson at 9. That's the former time slot of Fox News' second-biggest star, Megyn Kelly, who left the network in January to join NBC News.

O'Reilly's contribution was huge: A former anchor of tabloid series Inside Edition, he's an original Fox News star who signed on, along with the network, in October 1996, and became its public face with his combative style and partisan fervor. Lately, he's averaged nearly 4 million viewers a night, well ahead of Carlson and MSNBC's Rachel Maddow Show, and will leave a big hole to fill, which the network acknowledged in a memo to employees: "By ratings standards, Bill O'Reilly is one of the most accomplished TV personalities in the history of cable news. His success by any measure is indisputable." But the network told staffers it has "demonstrated again and again the strength of its talent bench." Carlson has been a formidable replacement for Kelly, surprising some analysts, and The Five's ratings have been solid, particularly for the 5 p.m. hour in which it now airs.

Yet part of Fox's calculus in determining whether to keep O'Reilly surely rested on his weakening financial contribution. Though he had recently renewed his contract for a reported $20 million a year, dozens of advertisers dropped their sponsorship of his show in the wake of an April 1 New York Times story that exposed additional harassment claims. But the controversy also appeared to rally some of his supporters, giving him a ratings lift. (In a statement, O'Reilly said "it is tremendously disheartening that we part ways due to completely unfounded claims.")

Like its competitors, Fox benefited from a Trump bump during the election: Prime-time ratings were up a whopping 36% last year, to an average of 2.5 million viewers, more than the combined total of CNN and MSNBC. The gains extended past Inauguration Day, as Fox climbed to 2.9 million in the first three months of this year.

Branding consultant Allen Adamson predicts "short-term pain (and) long-term gain" from O'Reilly's ouster. "There will be some outrage among his fans, but most of his viewers are attached to the network, not the show," he says. If the network had allowed the controversy to linger — especially in the wake of its firing last summer of its founder, Roger Ailes, over similar charges — there'd be "more potential damage to the Fox News brand."

The network's supporters are loyal, because it has "a point of view that the audience agrees with," says Stacey Schulman of ad firm Katz Media Group. Few are likely to defect to CNN or MSNBC in protest: "There aren't a lot of other places to go." And with O'Reilly gone, she says, many of those advertisers will feel more comfortable about returning. "If you don't have them boycotting you anymore, it's easier to make money."