Jane Hall, an American University professor and former Fox contributor, who noted that it will take a while to see whether his loyal audience sticks with O'Reilly's replacement.
O'Reilly's departure creates new challenges for Fox →
"This is a surprisingly quick and strong exodus of advertisers," said Jane Hall, a professor at American University's School of Communication and a former Fox media analyst.
Will Bill O'Reilly survive advertiser defections? →