So why don't we make it illegal for politicians to lie? It seems much fairer. After all, corporations aren't allowed to put out misleading ads, so why should politicians?

It's a smaller harm if I buy diet products that don't work than if I vote for a politician who does the exact opposite of what he promised. Yet only the former is illegal.

Here we have Donald Trump's 'Contract with the American Voter': https://assets.donaldjtrump.com/_landings/contract/O-TRU-102.... How much of this did he accomplish?