This past week, Randall Woodfin, a young Alabama city attorney, unseated a two-term Democratic incumbent to become the mayor of Birmingham. Mr. Woodfin’s campaign, which was committed to Trump resistance, brought him national attention and successful fund-raising in New York and Washington. Central to his progressive platform was a proposal to drive up Birmingham’s minimum wage, after a move last year to bring the city’s rate to $10.10 an hour was quickly undercut by the State Legislature. Mr. Woodfin maintains a more ambitious agenda, to eventually get the city’s minimum wage to $15 an hour.

“The Fight for 15,” as the movement is known, began in New York five years ago, when 200 fast-food workers marched to demand $15 an hour and the right to unionize from their employers. Since then, the movement has spread to 300 cities around the world and won various political and corporate victories — last year Gov. Andrew M. Cuomo signed legislation that would secure a $15 an hour minimum wage for all workers in New York City by the end of 2019; in September, Target announced that it would raise its pay rate from $10 an hour to $11 right away and to $15 in three years.

The logic of $15 an hour follows thus: presuming a 40-hour workweek, a family of three (a single parent with two children, for example) would, at that rate, earn an annual salary of $31,200 which is approximately $10,000 more than the amount at which the government officially designates a family of that size as poor. For years though, antipoverty advocates have argued for different standards to assess need.