Ross Douthat spends an entire column valorizing the effect of third parties on the political system without addressing the primary reason we do not have them.
In political science, we have what is known as Duvergé’s Law. It is not a real law by scientific standards, but it is about as close as political science has come. Basically what it says is that single-member districts (first past the post elections where only one candidate wins) will encourage a two-party system while multi-member districts (seen in proportional representation) will encourage multi-party systems.
Third parties exist in the U.S. and even occasionally have political relevance (such as NY-23 this year or in the spoiler role of Ross Perot where they aren’t going to win but still skew the election from a pure two-party result), but there has never been a period of extended legitimate three party competition. A party may rise for one or two election cycles but inevitably it either collapses or takes the place of one of the existing main parties as it collapses.
Sure, there are some notable exceptions. Canada’s first past the post system has found itself in a period of persistent minority governments in part due to the gains of a variety of third parties, namely the Bloc Quebecois. This succeeds primarily because the cultural distinctness of Quebec have allowed a regional party to become one of the main parties in those districts. The United Kingdom has also witnessed an extended role of the Liberal Party in addition to Labour and Conservative Parties.
At the end of the day, a first past the post system will weaken if not outright defeat any ability for a third party to succeed in any consistent way. Even in Canada and the UK, these electoral rules underrepresent the third parties. Voters are often rational enough people, and the value of casting their vote for their preferred party, when they know that party will lose is typically less than the value of casting it for the preferred option of the main two. Only when a third-party candidate establishes competitive legitimacy do most consider casting a vote away from the D or R.
If we are to seek more third party competition, and I certainly think we should, we aren’t going to accomplish it by talking about how awesome it would be. The way to bolster third party competition is to move away from single-party districts to proportional systems of representation at all levels of government.
