For decades, public health advocates chipped away at the influence of Big Tobacco with measures aimed at discouraging cigarette use. But the bitter legal and political battles were just a prelude to the unfolding climactic clash that could determine the fate of smoking and whether these companies adapt or falter.

U.S. health officials have launched the most aggressive attack by far on cigarettes: Twin government proposals would ban menthol-flavored cigarettes and would limit nicotine levels to make traditional smoking less addictive. At the same time, the government is slowly embracing vaping as an alternative by authorizing the sale of some e-cigarettes, [...]