More background on this “non-partisan” commission.

The CPD was established in 1987 by the chairmen of the Democratic and Republican Parties to “take control of the presidential debates”. The commission was staffed by members from the two parties and chaired by the heads of the Democratic and Republican parties, Paul G. Kirk and Frank Fahrenkopf. At a 1987 press conference announcing the commission’s creation, Fahrenkopf said that the commission was not likely to include third-party candidates in debates, and Kirk said he personally believed they should be excluded from the debates.

It is not non-partisan. It is bipartisan. That’s an important difference. Saying that it’s nonpartisan is misinformation.

Third parties have often criticized exclusion of their candidates from debates, due to the CPD’s rule (established in 2000) that candidates must garner at least 15% support across five national polls to be invited to the national debates. The last candidate from outside the two major parties to participate in a CPD-sponsored debate was Ross Perot, who polled sufficiently high in his 1992 presidential campaign to debate George H. W. Bush and Bill Clinton in all three debates; Perot’s running mate, James Stockdale, also participated in the vice presidential debate. When Perot ran again in 1996, the CPD declined to invite him to the debates, finding that the Reform Party candidate had no “realistic chance to win” the election.

So, it’s an organization run by the two major parties that explicitly tries to keep third parties from participating in the debates.