A strong third party is rare in the history of the US. Strong is a relative term, of course.
Every time there is a significant third party in US history there seems to be a paradigm shift going on. Strong third parties are typically damaging to only one of the two major parties. A few examples:
The Whig party, strong from roughly 1834–56 was divided over issues giving birth to the Republican party. The third party was the Republican party in 1856. Divided, Buchanan (Democrat) became president.
The Republican party itself experienced a schism when its progressive wing didn’t want to give up power. Teddy Roosevelt (BM) ran against Taft (R ) and Wilson (D), effectively handing the presidency to the Democrats. The Democrats at that time also described themselves as progressives. The BM party was dominated by the personality of TR, so it did not remain a political force after he left the scene.
There are several examples of the Democrat party experiencing divisions that let to the Dixiecrats and States Rights movements. Ultimately, these movements were absorbed by the Republican party or re-absorbed by the Democrats after the peak of the civil rights era.
The election of 1992 is yet another example of the Republican party being divided. Many Republicans abandoned GHW Bush in favor of HR Perot, helping Clinton to win the Whitehouse.
In this last election, many disenchanted socialist-leaning Democrats jumped back on the bandwagon after years of voting for relatively small and insignificant socialist-leaning candidates that have inconsistently been able to appear on the ballot for the presidency. I know, I’m one of them and I know many others just like me. As long as the Democrats keep coming our way, there will be no need to break away. Those who think like I do sense that the Democrat party in the US has the potential to become more like its more palatable European cousin—the Social Democrats.
The Republicans are currently experiencing some soul searching. They are having a difficult time reclaiming the core issues that have kept this diverse group together in the past. I sense that the Libertarian-leaning and Constitutionally obsessed Republican wings of the party were very much disappointed in GW Bush, and regarded him as a “Big government” Republican. They tended to opt out of the last election because John McCain was viewed as continuing those policies. So, there is a potential splintering of the Republican party that could lead to a significant party by 2012. But this will only happen if the Republicans remain divided and are not successful in the H and S elections of 2010.
In the absence of a strong showing by Republicans in 2010, a third party will be born. Its core will be the two disappointed wings of the party that I mentioned before. I don’t believe they can muster any more than 20% of the electorate, despite the fact that the bulk of the Republican party members could potentially go their way. Why? Fear of being divided? Ironic, huh? Obama wins a second term in 2012, for this reason alone.