"Many of liberalism's most important ideas were lifted from these movements. Indeed, Milton Friedman has been heard to describe Thomas's Socialist Party as having been "the most influential party in the history of this country," as every one of its 1928 platform planks had later been enacted." (Friedman was referring to the fact that the New Deal Democrats had borrowed rather liberally from Thomas, just as Woodrow Wilson had borrowed from borrowed from Eugene Debs's Socialists, and Democrats under Williams Jennings Bryan had taken ideas from the Populist Party.)

from Why We're Liberals: A Handbook for Restoring America's Most Important Ideals - Eric Alterman