Every other election debates are held by a nonpartisan organization and a third party that meets certain requirements can also join.
They change the rules rather arbitrarily to suit their needs anyway. During the 2000 election Nader was excluded from debates under the new rule that the green party had to have gotten 5% of the vote (nationally) in the previous presidential election to quality. Some of the votes for Nader, that helped get Bush elected, were cast to make sure the green party got that 5% for the next election. They didn’t, it ended up at 4% and change, but the rule was changed for 2004 anyway so it wouldn’t have mattered.
They change the rules rather arbitrarily to suit their needs anyway. During the 2000 election Nader was excluded from debates under the new rule that the green party had to have gotten 5% of the vote (nationally) in the previous presidential election to quality. Some of the votes for Nader, that helped get Bush elected, were cast to make sure the green party got that 5% for the next election. They didn’t, it ended up at 4% and change, but the rule was changed for 2004 anyway so it wouldn’t have mattered.