The middle class is receiving less of America's total income, declining to its smallest share in decades as median wages stagnate in the economic doldrums and wealth concentrates at the top. A study released Wednesday by the Pew Research Center highlights diminished hopes, too, for the roughly 50 percent of adults defined as middle class, with household incomes ranging from $39,000 to $118,000. The report describes this mid-tier group as suffering its "worst decade in modern history," having fallen backward in income for the first time since the end of World War II. Three years after the recession technically ended,...