The answer to these questions lies partly in recent political history, partly in the difficulty in consciously making changes to the language. For several decades liberals did in fact try to wear the word liberal proudly, in spite of those who used it disparagingly. Progressive already existed in political parlance, but it had a broader, vaguer meaning than it does today and didn't necessarily imply an affinity for the left. In the 1980s, for example, the centrist Democratic Leadership Council called its think tank the Progressive Policy Institute. My guess is that the DLC aimed to evoke something along the lines of Teddy Roosevelt's bipartisan, reform-oriented "progressivism."
The degradation of the word liberal was gradual and, contrary to the oft-heard claim, not entirely due to the right's efforts. I think the process began in the late 1960s in reaction to the disillusionment and shattered dreams of the left. Around that time the term was undergoing a shift in meaning similar to what happened to a word like pious, where a formerly positive adjective comes to be used as a sneering description of those who fall short of the ideals they preach. Look, for instance, how Roger Ebert used it in his 1972 review of Sounder, a movie he defended against charges of liberalism:
It is, I suppose, a "liberal" film, and that has come to be a bad word in these times when liberalism is supposed to stand for compromise--for good intentions but no action. This movie stands for a lot more than that, and we live in such illiberal times that Sounder comes as a reminder of former dreams.By the 1970s, liberal was starting to be treated less like a political orientation than like a character type, describing an overzealous do-gooder who may even be a hypocrite and patronizing snob--someone much like the character of Meathead from All in the Family. When the right began using the word pejoratively, they were in part seizing on that stereotype. Of course there is a difference between the trait of "good intentions but no action" and the right's more malevolent view of liberals. But the image of the excessive do-gooder--and above all the connotation of weakness--prevailed.
For a long time, Democratic politicians were unsure whether to embrace the liberal label or run away from it. In 1988 Dukakis resisted it before finally admitting, late in his campaign, that "I'm a liberal in the tradition of Franklin Roosevelt and Harry Truman and John Kennedy." This comment was practically an apology, seeming to imply that liberalism had fallen from its lofty position in the ensuing decades. It was as if he was assuring the public, "I'm a liberal, but one of the good ones."
Indeed, when it came to presidential elections in the post-Vietnam era, it often seemed that the Democrats' victories rested on how successfully their candidates escaped the liberal label. This perception was probably delusional (Mondale and Dukakis were running against a popular administration, whereas Carter and Clinton were running against unpopular ones, and so their ideological character was probably not the determining factor in the outcome of those races), but it was a lesson the Democratic establishment took to heart.
The moderate, Third Way politics of the Clinton years disappointed many liberals at the time, but this was overshadowed somewhat by their disgust at the GOP's scandal-mongering against the president. By the end of the decade, when Clinton enjoyed sky-high approval ratings while the GOP ended up defeated and humiliated in its attempts to bring him down, there was a triumphant feeling among Democrats which, I believe, made many of them willing to forget (if not forgive) his policy betrayals.
This truce ended with the U.S. invasion of Iraq, an event that drove a wedge between the Democratic establishment and the left unlike anything seen in over a generation. As the left's antiwar position, dismissed at first as radical, eventually became the consensus not just within the Democratic Party but in the country as a whole, it damaged the establishment's credibility and made the left's early criticisms of the invasion seem prescient. I personally believe (but have rarely seen it expressed) that this factor was a large part of the reason for the DLC's demise. And of course it led to the rise of Obama, whose early opposition to the war may have been singlehandedly responsible for his narrow defeat of Hillary Clinton in the primaries. Despite GOP talking points about how he was the "most liberal Senator," the L-word commanded surprisingly little attention in the 2008 election, when compared with past races. Obama did, however, eagerly identify as "progressive," the first modern Democratic nominee to do so.
This new use of progressive arose during the boom in Internet political culture that came to be called the "netroots," dominated by activists who now had the tools to make their voice heard in a way that wasn't possible in earlier times. That was the main setting from which today's progressive movement emerged. Though they rarely explained why they preferred the term progressive, I believe there were two primary reasons: they associated liberal with compromise and moderation in the hated establishment, and they wanted to free themselves from the influence of conservative frames they felt had governed mainstream political discourse for too long. Creating a new word for themselves (or, rather, refashioning an old, nearly forgotten one) was a way of achieving that goal.
Naturally, the new progressives tended to be fairly young--people in their twenties when the millennium rolled around (basically my generation). Older figures who have come to be associated with the movement have had to adapt their language to the times. When I searched Paul Krugman's columns and books for the word progressive, all I found were some references to progressive taxation--until his 2007 book The Conscience of a Liberal, where he explains the difference between liberals and progressives:
The real distinction between the terms, at least as I and many others use them, is between philosophy and action. Liberals are those who believe in institutions that limit inequality and injustice. Progressives are those who participate, explicitly or implicitly, in a political coalition that defends and tries to enlarge those institutions. You're a liberal, whether you know it or not, if you believe that the United States should have universal health care. You're a progressive if you participate in the effort to bring universal health care into being. (p. 268)Although Krugman isn't defining the two terms as mutually exclusive, there is an echo of Ebert's association of liberalism with "good intentions but no action." Progressives, Krugman maintains, are liberals who put their beliefs into action. While that's an inspiring thought, I'm not sure it fits the way most people use these words. I assume Krugman bases his definition on the activist roots of the progressive movement, but by now (at least in my experience) there are plenty of self-identifying progressives not actively involved in the fight for liberal causes.
The linguist Geoffrey Nunberg rounds up various pundit theories on the progressive/liberal distinction before observing, "none of them has much to do with with how the labels are actually used." One problem I have with most of these theories is that they treat the categories as fixed and static. In reality, these words have had greatly varied meanings over time, and even within the same time have meant different things to different people. The fact that TR referred to himself as a Progressive while FDR considered himself a liberal doesn't shed much light on the differences between Clinton and Obama. With these caveats in mind, Nunberg offers his thoughts on what the progressive label is intended to signal today:
Far more than liberals, progressives see themselves in the line of the historical left. Not that America has much of a left to speak of anymore, at least by the standards of the leftists of the Vietnam era, who were a lot less eager than most modern-day progressives to identify themselves with the Democratic Party. But if modern progressives haven't inherited the radicalism or ferocity of the movement left of the 60's, they're doing what they can to keep its tone and attitude alive.I tend to agree. I just wonder how long this situation will last. As the new progressives grow older and the word progressive becomes more ingrained, its anti-establishment overtones may well fade. Eventually it may come to be a simple descriptor of the average left-leaning Democrat, occupying more or less the same place that liberal used to--before it was turned into an epithet.
Perhaps sensing this possibility, some conservatives in recent years have been trying to do to progressive what they once did to liberal. Glenn Beck attempted something of the sort in his 2010 speech to CPAC, where he linked today's progressives with the alleged evils of the early-20th century Progressive Movement. I doubt this strategy will work. These conservatives have grown too insulated from the mainstream to reach beyond their narrow audience (somehow I don't think most Americans would share Beck's outrage at TR's support for universal health care or Woodrow Wilson's creation of the Federal Reserve), and in any case the word progressive just doesn't carry the negative connotations that helped the right tarnish liberal. Whether conservatives or older liberals like it or not, progressive as a self-respecting term is here to stay.