Walmart still isn't paying workers enough, says one author calling for a $20 national minimum wage

The Fight for $15, a national political movement calling for minimum wage to be raised, began a decade ago with fast food workers walking off the job in New York City demanding $15 an hour. Starting this month, a handful of states actually hit that goal of a $15 minimum wage. 

Many major companies have also voluntarily raised pay to $15 or more in recent years — a multi-billion-dollar boost for hourly workers.  

But in a new book, author Rick Wartzman uses the story of Walmart to argue that corporate America – for all this change — is still paying workers less than it should.