Dan Rather, whose career at CBS News ground to an inglorious end 15 months ago over his role in an unsubstantiated report questioning President Bush’s Vietnam-era National Guard service, filed a $70 million lawsuit this afternoon against the network, its corporate parent and three of his former superiors. Mr. Rather, 75, asserts that the network violated his contract by giving him insufficient airtime on “60 Minutes” after forcing him to step down as anchor of the “CBS Evening News” in March 2005. He also contends that the network committed fraud by commissioning a “biased” and incomplete investigation of the flawed...