Ohio v. Thomas, 173 U.S. 276 (1898).

> Plus, I wasn't suggesting that we create laws that penalize federal officials for how they perform official duties.

You specifically proposed making them liable for breach of contract under state law if their official acts while in office did not comport with statements made prior to their election. Which is, exactly, punishing them for how they perform official duties.

> I wasn't suggesting that we prosecute them for how they do their job but prosecute them for false claims made to help them achieve that job.

If you abandoned your suggested contract model and instead wanted to make false campaign claims themselves actionable (rather than punishing for future actions that don't comport with campaign claims under a contract theory), I'm pretty sure that the First Amendment would be the problem -- the Constitutional bar for punishing acts of speech, particularly political speech, is very high, and there's almost no way that something trying to regulate based statements of the speakers future political intentions is ever going to meet it.

> Their actions in office would be evidence to a crime, not the crime itself.

Oh, and you want this to be a crime, now, not a civil offense (like breach of contract would be)? That makes it even less likely to be viable.