Allow third parties to speak at presidential and other political debates with less than 15% of the votes

Currently the US political system is run by two parties, Democrats and Republicans. For a healthy political system there needs to be more than just two sides to each issue. By lowering the amount of necessary support to 2% and increasing gradually as the election process gets farther along, by the end of the whole process maybe 15%, you allow for the people to choose between something more than black and white.
George Washington said that political parties would be the down fall of america. By only allowing two parties to speak you create an artificial monopoly of sorts toward the voters. People who are elected to either party are often at the extremes of the political spectrum, when the ideal politician is in the center and by allowing more parties to speak you can find the center.