When President George H.W. Bush famously reneged on his pledge at the 1988 Republican National Convention — "Read my lips: No new taxes" — that did not fall into any pattern of flips. Indeed, polls at the time showed Bush to be widely trusted. Still, the flip was a factor in Bush's tumble from extraordinary popularity to eventual defeat in his bid for re-election.
The Bush tax shift illustrates another theory about why some changed positions can be devastating: If you take a principled position, the public wants to see you stick with it, even if it's going to hurt.
"You should never completely trust someone until you have observed that person sticking with a losing side when they could have won by switching sides," said Blackwell, who teaches thousands of young Republican political wannabes at his Leadership Institute in Arlington, Va. "It's that willingness to lose that tends to separate the principled from the opportunists."
If the flip-flopper label seems to have been applied more frequently in recent years, that's in part because of more aggressive political ads, an accelerated news cycle and news coverage that is ever more assiduous about hunting for candidates' inconsistencies, said Brendan Nyhan, a political scientist at Dartmouth College who studies political scandals and spin.
In addition, as Thomas Mann and Norman Ornstein argue in their new book, "It's Even Worse Than It Looks," the increasingly ideological nature of both political parties has given rise to a quest for purity in which a changed mind makes a politician untrustworthy.
Both Obama and Romney "have changed lots of positions," Nyhan said. "But the press is going to punish Romney, because there's this perception of him as inauthentic, like with Al Gore: The elite press had a very cynical view of him as someone who just said what the public wanted to hear, and they just punished him and punished him for it."