I've been wondering for a little while about why Democrats were shedding the term 'liberal' in favor of the word 'progressive' to describe themselves. Apparently there is a history to the terminology, as I suspected there was, and they keep going back and forth on the terms. It's an enlightening read.

It comes from the Progressive Era. One of its intellectual and political leaders was President Woodrow Wilson. The Progressive Movement's chief aim was to centralize power by eliminating those pesky little concepts of separation of powers and checks and balances and escape the confines of a fixed constitution so that America could progress (not that it hadn't up to that point as evidenced by the abolishment of slavery and its rise as a world power).

Not surprisingly, the Progressive Movement's adherence to Darwinism gave birth to eugenics. Margaret Sanger, the founder of Planned Parenthood and a leader of the eugenics movement, advocated for a "stern and rigid policy of sterilization and segregation to that grade of population whose progeny is already tainted or whose inheritance is such that objectionable traits may be transmitted to offspring." In 1927, the U.S. Supreme Court upheld a law permitting forced sterilization in which Oliver Wendell Holmes proclaimed: "Three generations of imbeciles are enough." The culmination of eugenics was the rise of Nazism in Germany and the Holocaust.

To escape the baggage of the term progressives, they started calling themselves liberals. Today's liberals, like yesterday's progressives, believe wholeheartedly that the answer to all of societies problems lies in the use of government by enlightened leaders to effectuate progress and view constitutional constraints as archaic and quaint.

You can find a list of people who advocate progressivism here.