Every four years someone usually comes along to be a third party candidate for President of the United States: Nadar, Perot, and now Jill Stein and Gary Johnson. While one can respect anyone who takes the honest time and energy to run for the Oval Office, the chances of those who run that are not of the Major Parties are slim to none.
If you look at any Local, State or Federal Government most of the times they will either have a D or R beside their names. They have a base of power, which these Third Parties sorely lacks. However, in some miraculous fluke that the stars align just right and we have a President Johnson or Stein that is just one branch of the Government, they still have to deal with the contention of a Democratic Senate and a Republican House. There is only so much that a President can do without Congress' help, its how the Constitution has set up our Federal Government.
We can taut media, or money but in any case these parties that the Third Party Presidential Candidates have not done the one thing that has made the Democratic and Republican Parties so successful. They didn't start small. These Third Parties seldom work on a local level as a movement to change the Local Government or the State Government. When they do its usually an unorganized mess because quite frankly the leadership is seldom there. When they do have a successful run, they have a tendency to betray the people who supported them by making bargains with one of the two major political parties. Until they have proven their ability to effectively run a local campaign it hardly seems pragmatic to vote for someone who will not have much in the way of support from the Legislative Branch of the Government.
On a personal note for this short soapbox, I have considered voting for Independent candidates in the past: Jackie Green for Mayor (who is one of those who betrayed his supporters) and Gatewood Galbraith for Governor whom I did vote for this past election. Back in 2000 I considered Nadar, until the whole Nadar/Gore voting trade came up (which in my mind was just another betrayal).