TRIPP MICKLE, The Wall Street Journal, Updated March 26, 2015 12:16 a.m. ET Paul Frohman smokes an electronic cigarette outside an office building in downtown Los Angeles in January. California health officials declared e-cigarettes a health threat that should be strictly regulated like tobacco products. PHOTO: ASSOCIATED PRESS The U.S. government for the first time is taking aim at electronic cigarettes in an advertising campaign, challenging their use as...