John Sides highlights how little it has changed over time:
Two features of this graph deserve emphasis, I think. One is how poorly the trends conform to prevailing narratives about how the parties have changed. In particular, there is precious little evidence that Americans perceived the Democratic Party’s “re-boot” in the late 1980s and 1990s—when many observers believe that the party moved to the center under the influence of the Democratic Leadership Council and Bill Clinton. This is one reason why I’m skeptical that ideological “re-branding” is all that consequential.
That skepticism is even more justified by the second, and overriding, feature of the graph: just how little change in perceptions there has been over time. The GOP is perceived to be only slightly more conservative than it was forty years ago. As of 2008, the Democratic Party was perceived to be as liberal as it was when it nominated George McGovern. As of 2012, it was perceived to be only a bit more liberal than in 1972. We can have an argument about whether the Democratic Party has shifted left or right. The point is that the public doesn’t see much of any shift.
The Dish 