Indeed, 43 percent of Democrats called themselves liberal in 2013, compared with just 32 percent who said this 10 years ago. The shift toward liberal identity has come about equally from moderates (minus five points since 2003) and conservatives (minus six points). By contrast, the trend line for liberal identity among Republicans and independents is flat.
The liberal shift of Democrats coincides with improving fortunes for the party, including a long-term drop in popularity of Republican president George W. Bush, the Afghanistan and Iraq wars and the two elections of President Obama. It also may be related to growing public support for socially liberal policies and a renewed political focus on income inequality beginning with the Occupy Wall Street Movement.
As Gallup's Jeffrey M. Jones points out, the findings "confirm the tendency for Americans who identify with the two major parties to be more ideologically homogeneous than was the case in the past, a tendency that appears to be matched by the increasing polarization between Democratic and Republican members of Congress."
But beyond an actual policy shift, it's possible the stigma surrounding the word "liberal" has also worn off. Only 39 percent of Americans had a "negative" impression of the word "liberal" in a 2011 Pew Research Center poll, compared with 50 percent who saw the term in a positive light.