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"Liberal" has always, to me, referred to matters economic: Regulating business and the larger economy, funding social services, a tax policy that's, uh, progressive, and so on.
While "Progressive" has (in addition to Liberalism) embraced causes like civil rights, environmentalism, and opposition to the kinds of wars that have mainly been about defining or building empire, all things that were not even particularly correlated with "Liberal" politics until the mid-1900s.
So I like both terms, and I also like any discussion that breaks through the labels and gets into the substance of each, which I think is encouraged by having more than one label to rally around.