What weaknesses could someone exploit to manipulate this "Approval plus RCV" electoral system?
Question
I know that there must be ways that this system can be manipulated, but I'm having trouble figuring out what they are. I imagine that, since I created this system, I'm simply too close to it to see where exactly it would go wrong. For the story I want to write, someone (who, exactly, is yet to be determined) will be trying to manipulate the system to their advantage, so I need to figure out where the weak points are.
But at the same time, if the weak points are too obviously weak, I think it would be beyond the reader's reasonable suspension of disbelief for me not to fix them to a certain extent. I need a system that's reasonably sturdy for this person (or group of people) to still make a serious attempt to manipulate it and I am hoping that, with minimal tweaking, this is the system that will get me there.
To re-phrase the same question: What attack vectors exist in this system that a "bad actor" could exploit to their own advantage?
One potential angle, which I was recently reminded of (thank you @Mark), that I'd like a more knowledgeable person than myself to expand upon is Arrow's Impossibility Theorem. While this system certainly wouldn't have a dictator, I'm not yet very confident in my ability to thoroughly judge the other three criteria.
Everything beyond this point is a description of the system as I currently imagine it. I have many ideas to expand upon the government structure and the nature of checks and balances in this world, but I am trying to keep this down to only the relevant information. Feel free to request any such omitted details that you think may be relevant and I will edit to include them, if necessary. 161
Assuming that I can appropriately tweak this system, I plan to ask further questions regarding the other aspects of this government I've envisioned.
Election Schedule
Elections are regularly scheduled, not called at the whim of the current party or parties in power.
Ballot
At its core, the voting system in this fictional world is a combination of approval voting and ranked-choice voting. Voters can approve of as many candidates for an elected office as they wish and must rank, at the very least, all of their approved candidates (although they can rank any/all of their unapproved candidates, as well).
I currently imagine that the ranking of unapproved candidates would, to voters, seem like a vote of "tolerance" rather than "approval." In other words, this is where voters would be ranking the "lesser evils," in their opinion, among the candidates. Ballots on which voters rank some candidates but approve of none will still be accepted, as will blank ballots with no rankings or approvals. Each of these "statement ballots" will have meaningful effects upon the election of candidates to office and, to a certain extent, their powers while in office.
Step 1 (Approval)
Once ballots have been submitted and the election workers are beginning to process the votes, the first piece of data they will be concerned with is each candidate's approval rating. Depending upon the number of seats per constituency an office elects, an approval threshold will be set (outlined below) beyond which a seated candidate will be said to have a "mandate." Whether or not a candidate has a mandate is based solely upon original approval and not subject to subsequent adjustments through the "satisfaction" process outlined in Step 3.
So long as at least one candidate is beyond the approval threshold, only those candidates beyond the approval threshold will be considered for being seated at all. If only one candidate is beyond the threshold, then they immediately win the seat in question without considering voter rankings at all. If there are still seats left to be filled, but no remaining candidates are beyond the threshold, then all candidates will move on to the next step, where they will be judged based on voter preferences.
Importantly, if a candidate is seated without a mandate, they will have certain limits placed on their powers in office and may even face electoral consequences such as a shorter term length or easier recall.
Single-Seat: For any office that elects only one member per constituency, which I will mostly limit to the Executive branch, candidates receive a mandate when they surpass 50% approval.
Referenda: For all intents and purposes, votes on various competing referenda would follow the same process as Single-Seat offices, merely replacing candidates with the various legislation under consideration. They would need to surpass 50% approval to receive a mandate and, if no legislation receives such a mandate, may be subject to certain limits as prescribed by the legislature.
Multi-Seat: For any office that elects multiple members per constituency, an approval threshold will be set equal to the reciprocal of the number of seated officials. 161