There are laws about lying about public officials, and essentially it's legal if they can claim there's some type of "grey area."
Hmmm...well, I don't know how the law works in that regard. It just seems to me that if they really wanted to, they could put some heat on people who boldfaced lied about them.
But the fact that public figures rarely, if ever, DO engage legal actions in that regard reinforces your point.