Jonathan Chait of The New Republic explains in a few succinct paragraphs why the flip-flopper label is routinely applied to Democrats in presidential elections:
In the late 1980s, the popular revolt against government that had bubbled up in the mid-'60s began to peter out, sapping the power of straightforward anti-government appeals. And, starting in 1992, Democrats ruthlessly purged nearly all their political liabilities by embracing anti-crime measures, welfare reform, and middle-class tax cuts, and, more recently, by abandoning gun control. What's left is a political terrain generally favorable to Democrats, which has, in turn, forced Republicans to emphasize the personal virtue of their nominees.
And so, every four years, we have a Democratic candidate campaigning on health care, the minimum wage, education, Medicare, or Social Security, and a Republican candidate campaigning on themes like Trust, Courage, and so forth. President Bush in 2004 was explicit about his elevation of character over issues: "Even when we don't agree," he would say, "at least you know what I believe and where I stand."
The details of the Republican character narrative vary a bit from campaign to campaign. (In 1992, 1996, and 2008, Republicans waxed rhapsodic about the moral virtues inherent in military service; in 2000 and 2004, they played them down.) The alleged flip-floppiness of the Democratic nominee, though, is a hardy perennial. Flip-flopping is a simple accusation that campaign reporters can sink their teeth into. Moreover, there's always grist for the accusation, because getting to the position of running for president without changing your stance on a few issues is essentially impossible.
And, so, whatever two or three issues the Democratic nominee has changed his emphasis on are inevitably blown up into a devastating character indictment. The Charles Krauthammers and Sean Hannitys of the world can be counted on to whip themselves into a moralistic frenzy against the feckless Democrat. And news reporters will stroke their chins and ponder, because the question is being asked: Just who is Obama (Kerry/Gore/Clinton), anyway? Yes, he may have a detailed platform on domestic and foreign policy, but do we really know anything about this man?
But, as Chait goes on to point out, John McCain, who has changed many of his positions since he failed to win the Republican nomination in 2000, gets a pass on the issue of flip-flopping.
It's amazing how shallow our political life has become.