I think it could be as simple as party x claims they will do thing a, b, c and then after their term in power you assess if they achieved those things. The parties who make the claims will need to back up those claims with real milestones that would become performance indicators of partial or full success. The milestones must be easy to assess and leave no room for interpretation. Just like in a legal contract, if you make the wording too vague and hard to interpret, then your contract won’t be enforceable in court.