I am kind of a one-trick pony around here about this, but once more into the breach, dear friends.
We have a stable two party system because of our electoral rules. Other democracies have different electoral rules, and these drive different outcomes.
It is extremely, extremely, extremely rare for a plurality electoral rule to generate anything other than a two party system.
There are real advantages to this that we tend to ignore. Two parties means that the winner typically governs with the consent of a simple majority of voters. This is, to most definitions, pretty fair. But imagine a parliamentary government with proportional representation. This allows a winning coalition, and even a prime minister, to run the show with a small fraction of actual votes. Yes, you have lots of parties to choose from. By the same token, less consent of the governed is required to own the government.
For all of the agitation people make about third parties, I am not clear how many people are actually willing to make this trade-off.
It’s pretty easy to make a case that this can also be unfair, leading to a system in which the guy with 51% of the vote gets 100% of the power.
This ignores the fact that, in many (most?) parliamentary systems, a minority government can only govern effectively by reaching out to other parties and taking account of other people’s interests. Some might argue that a need to compromise, and to enter into power-sharing arrangements with groups that represent a broader section of the population, is not necessarily a bad thing.
That’s the whole point, really. There is no perfect voting rule, and increasing fairness in one way will typically impair rationality or equity in another. How it shakes out reflects the values and priorities of the society that creates the rule.
Whether or not this is actually a good thing is very much an open question. It is also not at all clear, despite the rhetoric, when broad coalitions actually benefit from power sharing. The formal literature on parliamentary governments is particularly huge: Japan and the Netherlands get a lot of attention due to their rules and some interesting properties of their governments. Though it is a little outside my comfort zone, I’d be happy to explore it in another thread.
Maybe the answer is not a third party, but a weakening of the party system. Unlike a parlimentarian system, there is no real need for parties in the US.
I’d like to see no public money going to support any party functions. Get rid of party registration and open up the primaries. I’m not even sure we should have ballots list party affilliation.
I’d like to see more Bernie Sanders, McCains, and (as much as I hate him) Liebermans.