Sorry if this has already been posted.
I have browsed through many threads on DU over the years that sought clear definitions of the words "liberal" and "progressive." I don't know if te information provided by the bloggers in the OP title will clear anything up or add to the debate, but for what it's all worth, the posts are actually worth your valuable time:
The Flip. Until FDR, "progressive" was actually the most common term used to describe the mainstream of American leftism. In what can be considered an early example of triangulation, FDR instead chose to call himself a "liberal," thereby poaching some of Hoover's turf while also distancing himself from the left-wing label "progressive." FDR thus changed the meaning of both terms in American political discourse, as the "progressive" label was rendered fringe left-wing, and the "liberal" label was tied to the economic policies of the New Deal instead of the laissez-faire and corporatist policies. From what I understand, Hoover was so outraged over FDR calling himself a liberal during the 1932 campaign, that Hoover challenged FDR to a debate entirely over who was the true "liberal" in the race. It is also important to note that when former Vice President Henry Wallace broke from the Democratic Party in 1948, he took up the banner of the "progressive" party. After that debacle, people did not call themselves "progressive" for some time.
The 1990's revival. After nearly fifty years in the post-Wallace wilderness, the term "progressive" saw a revival in our political discourse in the 1990's primarily from two sources. First, "third way" triangulation types such as the DLC took to the term as a means to avoid being labeled as "liberal." Second, left-wing creative class types, at first primarily in the Bay Area, took to the term in order to disassociate themselves with the exiting "liberal" political infrastructure on both ideological and identity-based grounds. It must have been unpalatable for the wildly successful, and generally cutting edge, entrepreneurs of the Bay Area to self-associate with an ideological term that appeared to be old-fashioned and failing.
The New Big-Tent Term. Entering 2007, "progressive" appears to be the new and emerging "big-tent" term for the American center-left. The term is used just as comfortably by New Dem types as it is by the Democratic Party's left-wing. Whether or not this has drained it of any significant meaning is open to debate. Whether or not it still has any significant difference from the term "liberal" is also open to debate. It certainly appears to have morphed into something of an empty vessel term that an increasingly large segment, if not the majority, of the left and center-left political activist community feels comfortable self-identifying with. That is a good thing, because it allows us a sense of unity we lacked when many would call themselves moderate and many would call themselves liberal. However, it is difficult to tell what degree of resonance the term has outside of the universe of political activists. Pollsters like to use the same question for decades, and thus are not ready to start including the term "progressive" in ideological self-identification questions anytime soon.
http://www.mydd.com/story/2007/1/2/12413/90231and...
Chris' history lesson on the subject is basically sound if a bit incomplete. He's correct in saying that late-nineteenth century Democrats (at least up until the fusion with Populists in 1896) were "liberal" in the European sense of favoring laissez-faire economic policies; there's a good reason that ur-libertarian Ayn Rand regarded Grover Cleveland as the beau ideal of American political history. But they did not always think of themselves as such, given their espousal of states-rights and constitutional strict-construction doctrines; regular southern Democrats in particular called their party "conservative" through most of the nineteenth century.
Likewise, "progressive" was not universally used as the self-identifier of the center-left prior to the New Deal. The term was often used by business interests who thought of advanced capitalism as a historically determined trend. And many Populists, who often argued they were restoring a pre-capitalist Jeffersonian political order, certainly didn't embrace the label of "progressive," either.
Chris is spot-on in noting that "progressive" became tainted by its association with the pro-communist (or at least anti-anti-communist) Left, especially in 1948. And he's also right in acknowledging that the revival of the "progressive" self-identification occurred almost simultaneously in two very different parts of the Democratic Party in the 1990s: the anti-war, anti-corporate, anti-establishment Left, and the New Democrat movement in the center-left.
I have one quibble with Chris' suggestion that New Democrats started using the term "progressive" (most notably with the establishment of the Progressive Policy Institute in 1989) "as a means to avoid being labeled as 'liberal.'" That suggests the terminology was purely cosmetic and non-ideological. In fact, the early New Democrats argued that "liberalism" had become temperamentally reactionary, consumed with defending the dead letter of every single New Deal/Great Society program and policy, while sacrificing the spirit of innovation that made "progressives" progressive. The whole international "Third Way" phenomenon was not designed to produce a moderate middle-point between Left and Right, but instead a reformulation of the progressive mission of the center-left at a time when the Right was successfully battening on popular discontent with outworn social democratic programs. That's why many of us from the New Dem tradition heartily dislike the "centrist" or "moderate" labels, even though they are hard to escape as a short-hand for intra-party politics.
http://newdonkey.blogspot.com/