The American political system was characterized by the dominance of two political parties the Republican and Democratic Party. These two parties determined the political life of the country in the course of the 20th century and, today, they are still the only parties who compete for power. In such a situation, third parties were traditionally weak in the USA and they have never won Presidential elections in the 20th century, although the Bull Moose Party headed by T. Roosevelt had managed to won 27.4% of the popular vote at the Presidential elections of 1912 (Lewis, 1998).
In fact, the Presidential elections of 1912 proved to be the most successful for third parties, namely the Bull Moose Party, which was also known as the Progressive Party. No other third party could have won so much popular votes at the Presidential elections. However, there were other successful parties, such as the American Independent Party which won 13.5% of popular votes in 1968, or Reform Party, which candidate Ross Perot won 8% in 1996 and 18.9% of popular vote in 1992 (Lewis, 1998).
At the same time, some third parties totally failed Presidential elections winning less than 1% of popular votes, such as the Farmer-Labor Party which won 0.99% in 1920. In general, third parties normally won 1-3%. However, it does not necessarily mean that third parties are absolutely insignificant in American politics. In fact, they may play an important role, especially when the rivalry between Republican and Democrat candidates is close. In such a situation, votes of third parties could be crucial for the win of either candidates.
On the other hand, third parties cannot overcome barriers established by the two dominant parties and electoral process which prevents third parties from the win on the national level because of their inability to get sufficient representation nationwide.