Again, I mean practically.
Think of Wilson's policies. At the time, it was progressive to think segregation was justified based on racial superiority. Relative to now, not quite so much. Get this, though : there was a point in time where colored folks did share things with whites prior to Jim Crow. And that was ousted by the following generation after the Civil War.
But, by the means of progress, that was implemented by the lefties of the time. And what a way to progress the nation into the best union of peoples the world would have seen, wasn't it? Years of strikes, riots, and complaints from one citizen to another...yup, totally progressive...
I could suppose Communism was a sort of lefty notion, too, considering the premise was for the people, by the people. Not like anyone but the man himself intended to let it transform into a dictatorship.
That's why I'm not so fond of equating liberals as progressive thinkers. A lot of well-meaning policies may have hindered mankind's progress as a species, and one man's progress now is only relative to his era.
Hell, even the Progressive movement can only go so far before going beyond what's pragmatic for a massive nation, in terms of costs vs. safety and satisfaction.