If the U.S. minimum wage, now $7.25 per hour, had kept pace with its purchasing power high point in 1968, it would be $10.46 today.If it had kept up with worker productivity gains since 1968, it would be $21.72.

So says a well-researched white paper prepared by state Rep. Ryan Winkler and staffers for his Select Committee on Living Wage Jobs, and distributed Friday in advance of the Minnesota House's consideration of his bill to increase Minnesota's wage minimum to $9.50 per hour by August 2015.

Big state and federal tax cuts for the rich a dozen years ago are sometimes cited as the reason for growing income inequality in America. DFLer Winkler argues that a bigger cause is the political failure to regularly boost low-level wages, something that the U.S. market has demonstrated it does not do dependably on its own. "Wage stagnation is the single most important contributor to growing economic inequality in Minnesota and the nation," the paper says.

Minnesota has not increased its minimum wage since 2005; the federal floor was last raised in 2007. Meanwhile, the U.S. poverty rate grew from 11.3 percent in 2000 to 15 percent in 2011, and the share of U.S. incomes claimed by the top 1 percent has surged since the end of the Great Recession.

History teaches that a widening income gap invites social and political upheaval. Government is well advised to take reasonable steps to narrow that gap -- and it's hard to argue that a wage of $9.50 per hour is unreasonable.