I thought Ralph Nader and Ross Perot were in the national debates? Weren't they third party candidates?
Ross Perot was included in the national debates in 1992.
But Ralph Nader was actually barred from entry to the presidential debates in 2000.
And Gary Johnson of the Libertarian Party and Jill Stein of the Green Party were not in any national debates with Mitt Romney or Barack Obama.
In fact a debate between third-party candidates was held in Chicago sponsored by news outlet Russia Today and moderated by Larry King. This debate included Johnson and Stein, as well as Virgil Goode of the Constitution Party and Rocky Anderson of the Justice Party. The debate was streamed on YouTube and can be found there.
Buddy Roemer also ran for President, and sought the nomination of the Reform Party. Early in the election season, he was on "Morning Joe" on MSNBC and got a bit of national exposure that way, but he said in an interview of the podcast "Dan Carlin's Common Sense" he said how the executives at all the major media outlets refused to allow him on so as to give better chances to the candidates for the major two parties.
Also, it should be noted that presidential debates were overseen by the League of Women Voters in 1976, 1980, and 1984. However, they decided to end this, condemning the demands of the two-party system.
The League of Women Voters said:
The League of Women Voters is withdrawing sponsorship of the presidential debates...because the demands of the two campaign organizations would perpetrate a fraud on the American voter. It has become clear to us that the candidates' organizations aim to add debates to their list of campaign-trail charades devoid of substance, spontaneity and answers to tough questions. The League has no intention of becoming an accessory to the hoodwinking of the American public.
—League President Nancy M. Neuman, LWV October 03, 1988
In 1987, the Commission on Presidential Debates was created. It is not a government organization. Rather, it is a non-profit corporation created by the Democratic and Republican parties. It is funded by contributions from foundations and corporations.
Considering the Commission on Presidential Debates is controlled by both the Democratic and Republican parties, it is in their interests to prevent third-party candidates from getting any national exposure.
Which they do so however they can.
So our practice in conducting presidential debates is just as corrupt as everything else is in the United States.