I don't see how this is worse than FPTP. In FPTP, the candidate with the most votes just wins, even if that is only 15%. A second round for the two most popular candidates is still better than that.

The issue in your example is of course that both parties send all their candidates to the election, instead of just their most popular one, and that dilutes the vote, but the same would happen if they did that in FPTP.

It's only in systems like approval voting or instant run-off that parties can afford to send all their candidates.

> In FPTP, the candidate with the most votes just wins, even if that is only 15%. A second round for the two most popular candidates is still better than that.

In practice, most US elections are preceded by explicitly partisan primaries, and that's the status quo you should be comparing against.

But that's something that they can continue doing. There are many countries where they have a second round between the two candidates with the most votes, and in those countries, parties generally send only one candidate. And that's what they'll keep doing under this system, because they want their candidate to end up in the top-2.

So unless you actively ban any kind of candidate selection by the parties, that is what would also happen in the US.

I believe the particular design of the top-two primary allows anyone to enter the primary and list any party as their "preferred party." So the party might endorse a particular candidate, they can't prevent other candidate from getting on the ballot under their party name.

I think this is easily addressed by using approval voting in the open primary. (And this has the benefit of being extremely simple while likely getting all the benefits of IRV/Condorcet.) Any sort of RCV ends up so convoluted I think a lot of people will try to be strategic but completely misunderstand some edge cases.

> There is one thing that is worse than FPTP: The Top-Two Primary. A bunch of candidates run, if no one gets 50% then the top two vote-getters face off in a second round with no other options allowed.

Well, that is just plain two round system, it is pretty common and definitely better than FPTP. The bizzare outcome you describe may also happen with FPTP, you just need one candidate from party A and several candidates from party B. The solution is same as in FPTP system - each party endorses just one candidate.

>Well, that is just plain two round system, it is pretty common and definitely better than FPTP.

I would differentiate it from a two-round system in that voting takes place on a single ballot paper.

In two-round elections there is the ability to use the information about who is in the top 1 to cast the second vote.

In Supplemental Voting an elector has no information as to who's going to be in the top 2 when they cast the second preference.

Voting systems that serve to "moderate" voter preferences are anti-democratic. Sometimes an extreme policy is necessary to meet a challenge (e.g. climate change). A voting system should simply do its best to express true voter preferences. That's it.

Do you have a specific example where this scenario played out?

This happened in the 2016 Washington State Treasurer election

https://ballotpedia.org/Washington_Treasurer_election,_2016

Duane Davidson (R) won against Michael Waite (R) after 3 democrats split the vote in the primary:

    Republican Duane Davidson 25.09% 322,374
     Republican Michael Waite 23.33% 299,766
     Democratic Marko Liias 20.36% 261,633
     Democratic John Paul Comerford 17.97% 230,904
     Democratic Alec Fisken 13.24% 170,117

I'm not sure any of the alternative systems would have actually given a different result. Yes, the democrats have a majority of the vote, but transfer of support between members of a party is never perfect.

I'm also not sure if this is enough of a problem to try to solve preemptively, if there's one example from four years ago from a state-level election.

If outcomes in general are better, I'll take the risk that they're occasionally worse.

Well that raises the question why there were 3 Dems to begin with.

That's what we have here in France, which led to a right vs far-right second round in 2002, from which the traditional left never really recovered.

True. But it also prevented LePen. And before it produced Holland, regardless hoe bad a president he was, he was definitely from the left of the political spectrum.

that sounds like a problem with considering parties when voting, and trying to reduce the complexity of choice to a binary, rather than the merits of the candidates themselves.

Why would you have inner party run-offs in a public election anyway? Just have sort out their candidate far any given election internally beforehand. Then a Top-Two system is actually pretty nice, for direct mandates that is.