Stagnating wages and widening inequality are the central economic challenges of our day. Without wage growth, the gains from economic expansion — as measured by income and wealth — become increasingly concentrated at the top of the economic ladder in a self-reinforcing process that makes broad prosperity impossible.

With Congress unwilling to address those challenges, the states have picked up some of the slack. Currently, for example, 26 states and the District of Columbia have, or soon will have, raised their minimum wage above the paltry federal minimum of $7.25 an hour.

Even so, these more robust state minimums tend to cluster around $8 to $10 an hour, which is better than $7.25, but still lower than the $11 to $18 an hour that is needed to bring minimum wages in line with relevant benchmarks, including the cost of living, average wages and labor productivity.

That is where cities have come in, with mayors, city governments and grass-roots organizations emerging as the true leaders in efforts to raise wages from the bottom up.