MSNBC, once the also-ran, now the No. 2 cable news channel, has a new tagline that embraces its progressive political identity. The tagline, “Lean Forward,” will be publicly unveiled Tuesday, at the start of a two-year advertising campaign intended to raise awareness of the channel among viewers, advertisers and distributors. The tagline “defines us and defines our competition,” said Phil Griffin, the president of MSNBC, his inference being that the Fox News Channel, the No. 1 cable news channel and a home for conservatives, is leaning backwards. Fox’s best-known tagline is “Fair and Balanced.” Some of the new MSNBC ads...