Voters have been losing their taste for the war on drugs lately; in the past few years, states from Arizona and Alaska to California and Hawaii have moved toward making marijuana, in particular, a low priority for law enforcement, with first-offense possession cases often dismissed with small-time fines and medical-marijuana measures on the books in several states. But the initiative voters in Nevada will be considering this fall goes much further: The “tax and regulate” measure, whose supporters got it on the ballot by collecting 86,000 signatures, would allow anyone over 21 to possess up to one ounce for personal...