Ford? Easily explained by Watergate and the pardoning of Nixon, so let's set that one aside. Clinton's slide? Well, it's before a stained blue dress, so I'm guessing it was the gays in the military thing -- but that's just a guess without taking the time to look it up.
Does this slide mean much? Not really. Clinton was easily re-elected. Carter had no real change and he was defeated. But in terms of what people think, the Obama folks have to worry about momentum and the perception in the public that he's failed to follow through with his promises. The health care debate is weighing down his presidential approval ratings, but that's not going to go away. The talk radio guys slam him every day but relatively few people (20 or so million, already Obama haters) pay attention.
Public perception is fickle. Right now, if I had to guess on what people know about the presidency of Barack Obama, it's that he's not doing as well as they'd hoped. Maybe their expectations were too high after Bush.