"Social liberal" is the term used to differentiate them from classical liberals. Not social as in social issues, social as in socialism. It was meant originally to be a center-left ideology more palatable for the middle classes than traditional leftism.
Progressives, by the American definition, tend to be to the left of the social liberals. The Green Party is very progressive, as are Representatives Kucinich and Grijalva. It is similar to Canadian, Australian and European social democracy (NDP, Labour Parties, etc). Both have heavy working-class backing.
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