Every four years, the Commission on Presidential Debates (CPD) puts on a series of campaign commercials disguised as presidential and vice-presidential debates.
The CPD is, in theory, a not-for-profit organization "established in 1987 to ensure that debates, as a permanent part of every general election, provide the best possible information to viewers and listeners."
But the CPD is really just a scam the Republican and Democratic parties use to funnel illegally large "in kind" campaign donations, in the form of tens of millions of dollars' worth of free media exposure, exclusively to their own candidates.
A real nonpartisan, not-for-profit debate organization would use objective criteria for deciding which candidates may participate in debates. The CPD continuously refines its criteria with an eye toward ensuring that no third party or independent candidates qualifies for a microphone at a CPD "debate."