The biggest controversy so far to surround next Monday’s presidential debate at Hofstra University has come from the exclusion of Gary Johnson, the Libertarian Party candidate, who failed to make a long-set 15 percent polling threshold.

The rule is enforced by the Commission on Presidential Debates — which began as sponsor of these events in the 1980s, taking over for the League of Women Voters.

While it is common in different kinds of races for debate sponsors to set rules for participation — and then for the candidates left out to then complain, demonstrate and appeal in court — this debate over the debates has a unique look.

Whether or not you find them persuasive, Johnson and his running mate, Bill Weld, and their supporters raise some points worth hearing as they argue the call.

For one, the last third-party candidate to ultimately win a seat at the debate table, Ross Perot, was only around 8 percent at this time in 1992, according to the Gallup Poll.

As of Sept. 15, Gallup showed Johnson at about that same number.

The difference: Perot’s numbers rose to the 15 percent mark before that first debate 24 years ago where he faced Bill Clinton and George H.W. Bush.

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But that was because the first of their three debates would not take place until Oct. 11 — which, as it turned out, allowed Perot time to rise and make the cut.

This year, in contrast, all the faceoffs come earlier in the season, with the second and third debates on Oct. 9 and Oct. 19.

Of course, no one knows if Johnson or Green Party candidate Jill Stein, who’s running around 3 percent, can get their numbers to spike as Perot’s did, or when.

The Johnson camp further notes he has made the ballot in all 50 states — the first third-party hopeful to do so since Perot.

Ironically, the same polls now disqualifying Johnson and Stein also could be used to rationalize letting third-party hopefuls in.

That is, record numbers seem to distrust both Republican Donald Trump and Democrat Hillary Clinton — no matter what either of them say on Long Island next Monday — and may well seek alternatives.

Weld, the former Republican governor of Massachusetts, has been making a related point for weeks: that since the debate commission was established, the percentage of voters unaffiliated with the Democratic or Republican parties has jumped.

“So the rationale for having only an ‘R’ and only a ‘D’ is dissipating,” he told reporters last month.

Late last month, 59 percent said “no” when asked if Clinton is honest and trustworthy — and 62 percent said “no” when asked the same about Trump, according to an ABC News survey.

Over the weekend, Johnson, the former two-term GOP governor of New Mexico, called the debate process a “rigged game” as he campaigned in Seattle.

“Democrats and Republicans make up the presidential debate commission,” he said. “Fifteen percent is not the law. It’s Democrats and Republicans not wanting a Ross Perot on the stage again.”

For the record: Perot in 1992 ended up with nearly 19 percent of the national vote — though he won no electoral votes in what proved a decisive first victory for Bill Clinton.