> The key issue is that the candidates can say virtually anything they want irrespectively whether it's true or not.

A lot of the people who appear to believe a given politician's untruths don't actually believe them, but go along because they feel the untruths are a small "price" to pay for the larger goals they share with the politician. The liar is on their "side", after all.

This phenomenon - publicly believing or denying, and privately disbelieving - gets more extreme the greater the untruth. Basically, as long as they are in on the political lie, they don't mind being lied to.