(Bloomberg) -- In the age of rising income inequality, the task of preserving America’s middle class has been taken on by politicians across the ideological spectrum. A new report from Pew Research Center shows just how much the economic fortunes of this group have changed since the 1970s.

In every decade since then, the percentage of adults living in middle-income households has fallen, according to Pew, which is based in Washington. The share now stands at 50%, compared with 61% in 1971.

This matters because the "state of the American middle class is at the heart of the economic platforms of many presidential candidates ahead of the 2016 election," Pew researchers Rakesh Kochhar and Richard Fry wrote in their report. Meanwhile "a flurry of new research points to the potential of a larger middle class to provide the economic boost sought by many advanced economies."