Third party in the US? Not likely.

On a couple of the comment boards I sometimes frequent, that partisans of Nader and the Green Party (who ran a non-Nader candidate this time around) often like to argue that if everyone had voted for [insert third-party here]. The possibility of the Greens emerging as Iceland's largest party in the wake of the economic collapse here has some here anticipating a similar development.

Unfortunately, a bias towards a two-party system is hardwired into our constitution (I am deliberate using the small "c" here). Our first-past-the-post system enhances majority representation and a presidential system has a centripetal effect on party formation. This latter comes from the fact that a President can't be removed by a member of a coalition even if it had a party in getting him elected. Further, since a US President has to get a soiid majority of the electoral votes, that support must consist of running him as a fusion candidate instead of having one's own leader who could then cut a deal. A third-party could hope to throw an election to the House, but unless it had a solid presence there, it would wield little influence.

Comparisons to Mexico the UK and Canada don't help here. Mexico does currently have a three-party system but there are two reasons why the case isn't analogous. Mexico had a de facto one-party system for decades after the Mexican Revolution. That may have distorted the dynamic, especially as the "third-party", the PRD, only formed twenty years ago by people breaking away from PRI.

The decline of the PRI can be seen in its representation on the Chamber of Deputies. It has gone from having just over half the deputies in 1988 to about 40% in 2000 to just over a quarter in 2006. Likewise, its percentage of the Presidential tally was about half the votes in 1988 and 1994 down to about a third in 2000 to just under a quarter in 2006. This may very well parallel the process in the ante-bellum US with PRI as the Whigs and PRD as the Republicans.

Further, the Mexican system isn't quite the same as ours. 300 deputies are picked by a first-past-the-post system, 200 others by proportional representation.

Finally, a US President requires a majority of electoral votes (although this can be based on a popular plurality, in 38/56 elections, the winner had a majority of the popular vote). The Mexican Presidency only requires a plurality of popular votes. The majority requirement has centripetal tendencies.

The UK has a de facto two party system. I wouldn't call the Liberal Democrats in the UK a major party. Starting in 1945, the Liberal party and its successors have never had more than 10% of the seats in Commons and there hasn't been a coalition government in the UK since WWII. The regional parties aren't even remotely important. Further, the UK is a parliamentary system, therefore a third-party, should it actually get leverage, is in a position to bring down a head of government.

This dynamic affects Canada as well. Further, the one situation in which a third-party can thrive in such a system is when it represents a regional interest. That's because the first-past-the-post system disproportionately rewards geographically concentrated parties. You can see an example in the 1948 presidential election in the US. Both Strom Thurmond's Dixiecrats and Henry Wallce's Progressives received a similar percentage of the popular vote, about 2.4%. However, Thurmond's vote was concentrated in the South and he broke into the electoral vote count with 39 while Wallace had none. Wallace didn't get more than 9% of the vote in any state. Thurmond got from 50-87& in the states that he took.

In Canada, the Bloc Quebecois represents many, if not most, of the Francophone residents of Quebec. Likewise, what is now Stephen Harper's Conservative Party started out as Preston Manning's west-based Reform Party in 1997. Looking at the Canadian election results, it was in 2004 that the Conservatives, formed by a merger of the old Progressive Conservatives and the Canadian Alliance, the descendant of the Reform Party, became a national party on a large scale by winning about a quarter of the seats in Ontario, its first substantial lodgement outside of its western core area. Since then, it two largest parties have been the Conservative and the Liberal, with Blog Quebecois being a strong third. Thus, what we have is another example of multi-party results being a way station to the replacement of one "second" party by another.

It would require major constitutional changes in the US system for a third-party to become permanently viable; of those changes and their possibility, I will write later.