See, in order to actually do it, you rework the entire system top to bottom.
If politicians are in legally binding contracts, they won't be lying to all of us constantly.
The entire idea requires a completely different system than we have, with the existing system, they just lie with impunity, or were "wrong" about a subject they pushed, and see no negative effects of that at all. You or I do that at our jobs, and we're fired.
If you're suggesting that you simply cannot hold public officials to their word, because reasons that just isn't good enough. That's just acknowledging that we're letting them lie to the citizenry with no consequences at all.
If they're found to be corrupt, arrest and jail them. What we do now is abhorrent when it comes to the political class lying with impunity.