According to Pew Research “progressive” is now the most positively viewed political term in America. It is viewed more favorably than Capitalism, Liberal or Conservative. From Pew:
From a purely PR perspective this is a real coup for the modern so called “progressive movement.” In a relatively short period of time it has given people on the political left the most positively received political label in America.
Seeing the huge difference in how people view the term “progressive” and the term “liberal,” it is no surprise that progressive has become by far the more popular way for people on the political left to describe themselves.
While branding is not everything in politics, it is important. The fact that for much of the last few decades it was more politically risky for a Democrat to call her/himself a “proud Liberal” than it was for a Republican to call her/himself a “proud Conservative” must have had a subtle but real impact on our political discourse.
Of course good branding without a solid structural foundation creates its own problems. Since what the word “progressive” really means is still somewhat vague, many organizations and politicians have started co-opting the title.