Didn’t know that one - intersting. In politics, Duverger described the phenomenon in the aptly named Duverger’s Law. Without a change to proportional representation, it is rational for the voters to behave in way that de facto favors a 2-party system.
Duverger’s Law is what I learned years ago in a political science class and it makes intrinsic sense. At the same time, the UK’s third party is almost always mentioned as an immediate counter example. I believe (I’m not a Canadian political system follower) Canada also has First Past the Post (FPTP) but also has three major national parties right now (Conservatives, New Dems, Liberals) and has always had the Bloc as a major regional party (I haven’t followed Canadian news enough to know what the long term impact of BQ essentially losing every seat they held in the last election will be for that party’s continued existence in the Federal Parliament long term.)
I would opine that since both Canada and the UK have Westminster style Parliamentary systems you still see third parties because the tendency for FPTP to lead to two parties can be offset if the national government has a tendency towards occasional hung parliaments / coalition governments, so supporting a third party means you could actually end up having a real impact on government. With the American system of hard-divisions between three branches, a separately elected Head of Government and a strongly bicameral legislature there are no real opportunities for small third parties to help in coalition style governments.
The American political system is intended to keep fringe political ideas out of power. Those who support a fringe political idea see this as a bug in the system that needs to be fixed; the rest of us see it as a feature.
In American politics, fringe ideas enter the mainstream by being adopted by one or both of the two big parties. They don’t enter by being carried in by a third party.
I can’t recall which thread, but another doper made the point that most people, especially independents that decide elections, vote for the politician, not the party. Most politician reject parts of the party platform that are unpopular with their constituency. Once elected, these politicians then morph the party platform to better match their own positions.
So if you are at all close to one of the two major parties, you can either run under that party’s banner and pick up an automatic 25-35% of the electorate (on either side) that votes a straight party line, or you can run as a third party candidate and be assured that the 50-70% of straight party line voters (both sides) won’t even consider you even if you are running against two space aliens (Simpson’s reference). And if you run as a third party candidate you typically need petition drives etc. just to get on the ballot, which chews up a lot of the meager resources you might have. So you run as a Democrat or a Republican, and once elected, you can feel free to ignore the party’s platform and start trying to bend it to your will.
Except that at a national level for the past 20 years or so, republican party discipline is very strong…it is very hard for even a popular politician to buck the leadership. It really takes a sub-caucus, like the tea party freshman congressman, to shift that party much at all. The republican base tends to be less tolerant of change as well, demanding that candidates sign pledges on a host of the core issues.
This means that, all else being equal, center leaning “Third party” candidates tend to go with the Democrats rather than the Republicans, and this of course tends to degrade Democratic party discipline, which draws in more “third party” candidates. At least that was how it worked until the Tea Party came along. Now that those folks have some mass in the House, John Boehner can only wish that his Caucus was as unified as Nancy Pelosi’s former Democratic majority.
Anyway, the point is that if a third party has enough cachet with the electorate to be even close to viable, either the Democrats or the Republicans will end up absorbing them. It only takes a few percentage points to swing elections in a lot of places, so there is strong incentive to capture the vote of even rather small groups.
It used to be that socially liberal but fiscally conservative candidates were “moderate Republicans” while socially conservative but fiscally liberal candiates were “moderate Democrats.”
Both parties got rid of them. To be exact, the extremist, single-issue voters in the party primaries got rid of them.
You can argue that the moderates can and should outnumber the extremists, but what you’re really talking about is not three parties, but four:
Fiscal conservative, social conservative
Fiscal conservative, social liberal
Fiscal liberal, social liberal
Fiscal liberal, social conservative
Which means that liberals and conservatives will team up on specific issues. Then the extremists will tear the coalitions apart and we’re back to where we are now.