If you follow voting issues, or if you happen to live in California, you may be aware of Proposition 14, an initiative which seeks to replace party-based primaries in the state with the so-called "top-two open primary" (TTOP); top-two because only the top two vote-getters get to appear on the ballot for the general election, and open because its open to candidates and voters from all parties.
It's a terrible idea. Let me show you why, by means of a few thought-experiments:
#1: Party Hack
First, let's presume I'm an ultra-partisan party hack for one of the two major parites; all I care about is whether or not a member of my party wins the general election, and that a member of the other major party doesn't. What changes for me under TTOP?
Before TTOP, the only reason I cared about primaries at all was I wanted to candidate with the best chance to win the general election to come out of the party primary; typically, I tend to back someone who's a moderate, rather than an extreme, member of my party, so that they'll get some cross-over support in the general, and pick up the moderates and independents; but not someone who's crazy moderate, such that the "base" (read: extreme wing of the party) stay home on election day... which means I can actually back a much more moderate candidate than their grumblings would attest to (they'll come around; after all, they wouldn't want a member of the other party to win, would they?)
What's different for me with TTOP? To keep things simple, let's assume that the other party only has a single candidate in the TTOP. Well, I have a small problem: if my moderate is too moderate, then the base will abandon him for the more-extreme option. And then, fearing that the extreme candidate in my party and the moderate member of my party will be the top-two, my cross-over support starts to slip away. So I stand I good chance to see my moderate go down, and the general to be between my extremist and the other party's guy; and that's a contest that I worry I might lose.
On the other hand, maybe I pick up a lot of true moderates. As long as the primary voters really don't care in a fight between my extremist and the other party's guy, then they have nothing to lose in voter for my moderate. But there's two problems with that. One, they really have to not care which of the those two wins, and most moderates lean one way or the other. Two, actual moderate (or independents or what have you) aren't used to voting in the formerly party-only primaries, so I'll need to step up my get-out-the-vote game, while focusing it on an entirely new electorate. That'll cost me a pretty penny.
These two forces pull in opposite directions with respect to how "moderate" the final election winner will be. But which force is stronger? Which is more likely to come up? A lot of ink is being sacrificed over that debate, but the best analytical guess comes from The Center For Government Studies [PDF], who conclude that, averaged over time, there will only be minimal improvement. Sometimes you'll end up with a more moderate eventual winner, but sometimes you'll get the crazy. By "on average" though, it means we're adding a lot of variance, which is to say, randomness. But we don't want randomness, we want accountability, and transparency, and responsiveness. Randomness doesn't help anyone. Still, I have to play the odds, and no matter what, I back my moderate.
But what if the other party chooses to also run two candidates against my two candidates? Then things get a bit more complicated, because now there's the chance that neither of my guys makes it to election day. Now I need to do extensive polling, and advertise it widely, because I've got to make sure that, no matter which of our two guys we choose to back, we've all got to back him, because in this case, a split vote could mean we're out with no chance of recovery.
My instincts point me clearly towards a simple conclusion: it would be really nice if we could have a party primary before the open primary. Except that's, for one, illegal now, and two, kind of pointing out how ridiculously stupid this law is in the first place. And the problem only gets worse for me if there are more members of my party running; as long as there's more than one candidate not of my party, I need to do everything I can to limit the number of members of my party that run, and the one tool I have for this, a party primary, is gone.
If I'm a party hack, I don't really like TTOP.
Separately, let's consider the case where there's three candidates in the TTOP: my guy, the other guy, and a third-party candidate. I still need to do a lot of polling and advertising, because if the third-party guy is doing well, and is doing well at my party's expense, then it's similar to the case where the other party was running two candidates; I might be out before the general. This is the dream scenario that a lot of third-party backers are envisioning for themselves now, where they unseat a major party candidate and go into the final vote. But how likely is that? Thankfully, we already know the answer to that, because TTOP is functionally the same as another voting system we've looked at: instant runoff voting. And we know that, in many situations involving three candidates, IRV leads to spoiled elections, and spoiled elections lead to a two-party dominated system. Which means we get the "lesser of two evils" voters, and things keep working for us just as before.
#2: A Moderate Voter
On the flip side, the problems are equal, but opposite. I can try to vote for third-parties, but I still probably see a spoiler before I see a winner, which the party hacks will be betting on. So I'll try to vote for more moderate members of major parties; which is fine, unless both parties are running a moderate, in which case I have to do a lot of homework to make sure the moderate vote doesn't get split such that neither moderate goes to the general and we're stuck with a vote between two insane extremists.
Sound and Fury
So in the aggregate, what we find is an effectively identical average effectiveness (perhaps a smidge better, according to simulations), but one that's surrounded by a lot more random variance, and with a whole lot more money spent on polling and advertising; which is, again, the same conclusion as the Center For Government Studies came to. And really, do we want to enact a change whose most significant effect will be to make our elected representatives to be more dependent on their corporate financiers?
All in all, TTOP isn't worth the trouble. So if you're Californian, remember to vote NO on Proposition 14.