How do third parties influence American politics?

Historically speaking, third parties have had a limited influence on American politics. Currently, the two major American parties--the Democrats and Republicans--have deliberately crafted platforms designed to address most of the concerns of the voting public. However, it is possible for a third party to seize political advantage by successfully arguing that existing parties are not offering a sufficient solution to a pressing problem. In this way, third parties that gain momentum usually do so by aligning themselves with one particular cause, such as debt reduction or Immigration. By leveraging one specific argument, that resonates with an identifiable segment of the voting public, third parties can temporarily present themselves as fresh alternatives to the "stagnant" positions of Democrats and Republicans. Over the long term, however, it becomes very difficult for a third party to remain new in the eyes of the voter and failure to win office consistently makes it difficult to secure the funding needed to sustain a challenge to established parties.