With pot sold openly to any adult who wants it in Colorado and Washington state, marijuana advocates were hoping restrictions in other states would fall like dominoes this election season, opening the way for a push in Congress to change federal drug laws. They were not anticipating a multimillion-dollar wager against them by a casino mogul. Or a spike in voter anxiety amid bureaucratic stumbles in regulating the nascent recreational pot market. Or an unfortunate cellphone video from a rowdy frat bar called Boots N Buckles. Now, legalization measures are teetering in Florida, Oregon and Alaska, states where supporters were confident of victory only a few months ago. It's all...