Democrats have spent years raging about the rise of super PACs and the millionaires and billionaires who fund them. Maybe they should start laughing instead, because the largest super PAC in history may come to be best known for taking down the Republican candidate who may have had the best chance to win in 2016.

On Thursday, we learned that 35 percent of the money spent so far by the super PAC supporting Jeb Bush has been used to target the candidacy of his fellow Floridian, Marco Rubio.

According to Jeremy Peters of the New York Times, the anti-Rubio ad buys by Right to Rise (R2R) have totaled a staggering $20 million.

That’s $20 million out of the nearly $60 million through which the super PAC’s honcho, Mike Murphy, has burned since R2R began its spending spree six months ago.

Bush raised $103 million for R2R before he officially announced his bid. The day he declared in June, it became illegal for him or anyone on his campaign to communicate with Murphy or anyone at Right to Rise in any way about politics.

From then to now, Bush has gone from a high of 17 percent in the Real Clear Politics poll average in July to 5 percent today. In New Hampshire, the first primary state, he’s gone from 16 percent to 8 percent.

R2R’s efforts on Bush’s behalf haven’t borne fruit, to put it mildly.

Except for this: It may well be that R2R’s relentless assaults on Rubio helped stall the Florida senator’s rise in November and December.

Meanwhile, outside of a couple of polls in New Hampshire and South Carolina suggesting a little bit of Jeb growth, there’s very little evidence Bush has benefited during that same period.

There is method here. But there is also madness. And a kind of indirect patricidal fury.

The method is simple. Bush and Rubio are competing for the same type of voter in the same “lane,” and so Murphy wants the voters who prefer Rubio to change their minds and go for Bush. The R2R ads have highlighted Rubio’s missed votes in the Senate and the fact that he changed his position on immigration. (One also mocked Rubio’s boots.)

The issue is not whether R2R has the right to take Rubio to task or to focus on his negatives so that people might sour on him and go for Bush. It’s all fair game (well, maybe not the boots).

The real issue here is the intensity of the anti-Rubio assault. R2R largely remained passive, for example, as John Kasich and Chris Christie made frantic inroads in New Hampshire — and they’re competing in the same “lane,” as well.

Herein lies the madness.

In almost every poll, Rubio is running third, with Donald Trump and Ted Cruz well ahead of him. Given that both have relatively high negatives, you might expect Right to Rise to do what it could to soften Trump up some.

It’s simple logic. There are far more people leaning toward Trump than Rubio, and Trump is a rich target. If you shake a tree with more apples, a greater number might fall into your basket.

But Right to Rise has done relatively little in this regard — there’s been one TV ad making fun of Trump for getting his foreign-policy knowledge from “the shows” and a billboard in Iowa that read, “Donald Trump is unhinged.”

Here’s the thing. Mike Murphy — a hilarious and punchy guy with whom I’ve had a long friendly acquaintance that I suspect will not survive the publication of this column — is anything but crazy. But he is often angry.

And what’s been happening here is in part the flowering of a seed of rage that has been growing within the precincts of what insiders call “Jebworld” for a year.

I’ve been told by people in the know in Florida and elsewhere that Jeb’s campaign intimates (and Jeb himself, for all I know) believe strongly that, out of loyalty, Rubio should have passed on a 2016 run. Back in 1998, Jeb offered crucial support to Rubio at a very early stage in his career and along the way as well.

Rubio’s decision to run is therefore viewed as a deep personal betrayal. And I mean very, very deep — so deep that senior members of Bush’s staff last summer began calling Rubio “Judas.”

I’ve also heard that in attempting to raise new money for Jeb while Bush was sinking quickly in the polls a few months ago and convince others not to give to the other Floridian, Murphy was privately very clear that he was going to go for Marco’s jugular no matter what.

In other words: Maybe Jeb wasn’t going to be the nominee, but it for damn sure wasn’t going to be Marco, either.

It’s a political Oedipus complex in reverse.

jpodhoretz@gmail.com