Grist: NextGen Climate Action, the group founded by billionaire climate-action booster Tom Steyer, had submitted the ad to run on D.C.-area NBC affiliate WRC-TV during Obamas Tuesday appearance on The Tonight Show, with the aim of reaching the influential inside-the-Beltway crowd. But at the last minute Tuesday evening, the station informed NextGen that the ad wouldnt run after all, because it violated guidelines as an attack of a personal nature. The ad does feature an actor playing TransCanada CEO...