For Fox, O'Brien would be a far less risky choice than tried-and-failed hosts (Chevy Chase, Joan Rivers) of the network's past.

FORBES: Entertainment

His jokes are aimed at people who would never watch Bill O'Reilly's conservative rant of a cable news show on Fox, but who recognise Mr Colbert's obnoxious on-screen persona as a parody of Mr O'Reilly because they have read about Mr O'Reilly in the New Yorker.

ECONOMIST: Lexington

Michael Waller, appeared on Fox News' The O'Reilly Factor in his capacity as a professor at the Institute of World Politics.

CENTERFORSECURITYPOLICY: The Center's Waller on Fox News

In his report, Cabinet Secretary Sir Gus O'Donnell criticised Mr Fox for allowing Mr Werritty to attend certain meetings, including one with a defence contractor, without civil servants being present.

BBC: 'Naive' Werritty admits mistakes over links to Liam Fox

Furthermore, whether Fox's affiliate stations would be interested in bringing O'Brien to the network remains a big question.

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Early on Tuesday evening, a shocked-looking Bill O'Reilly, a firebrand conservative talk-show host, went on the Republicans' favourite news broadcaster, Fox News.

BBC: US election: Republicans must change or die