With Jeff Zucker taking over at CNN, the network's managing editor says he is quitting. Mark Whitaker is a former Newsweek editor who also worked at NBC. He said in a memo to the staff Tuesday that with a new leader who has his own "forceful ideas," he thought it best to step aside. CNN says Mr. Zucker will take over Mr. Whitaker's role overseeing the editorial content of the U.S. cable news network, which is struggling with a ratings decline. Mr. Whitaker joined CNN in 2011 as executive vice president and managing editor, responsible for editorial content. Prior to that, he was the Washington bureau chief for NBC News. He says he is proud of efforts to expand CNN's programming, including upcoming weekend shows with Morgan Spurlock and Anthony Bourdain.