As if the presidential race weren’t kooky enough, now the New York billionaires are rumbling.

Donald Trump lashed out at Mike Bloomberg on Friday — even taking a crack at his diminutive stature — after the three-term mayor labeled him a “dangerous demagogue” during his speech at the Democratic National Convention Wednesday night.

“ ‘Little’ Michael Bloomberg, who never had the guts to run for president, knows nothing about me. His last term as Mayor was a disaster!” Trump tweeted Friday.

In a second tweet, the Republican nominee wrote: “If Michael Bloomberg ran again for Mayor of New York, he wouldn’t get 10% of the vote — they would run him out of town! #NeverHillary.”

It was a far cry from 2015, when Trump was quoted as praising Bloomberg while taking a slap his successor, Mayor de Blasio.

“We miss Michael. There’s a big difference, you notice? Everyone’s talking about it,” Trump told the Hollywood Reporter.

And a video clip tweeted out by Bloomberg’s former deputy mayor, Howard Wolfson, shows Trump shaking the then-mayor’s hand at a 2013 event and saying: “You have been a great mayor . . . I mean, this guy is fantastic.”

Now Trump’s attack could awaken a sleeping giant — Bloomberg’s wallet.

The Bloomberg camp was coy on whether the media mogul would dip into his estimated $48.2 billion fortune to boost Hillary Clinton, whom he has endorsed.

“It’s not something we’ve had any discussions about,” said spokesman Stu Loeser.

But Bloomberg has put his money where his mouth is before.

The Post found in November that he spent $72 million to help candidates and pet causes over the previous four years. He was a winner in 67 percent of the races and ballot initiatives in which he donated more than $10,000.

A former Democrat, Bloomberg was elected mayor in 2001 as a Republican but switched his affiliation to independent.

Before backing Clinton, he was reported to have been considering his own presidential run to stop Trump, with whom he disagrees on gun control, climate change, immigration and trade.

Bloomberg apparently blindsided Trump with his televised convention speech Wednesday.

“Trump says he wants to run the nation like he runs his business. God help us,” Bloomberg had told the crowd in Philly.

“I’m a New Yorker. I know a con when I see one . . . The richest thing about Donald Trump is his hypocrisy . . . We must unite around the candidate who can defeat a dangerous demagogue.”

He said he backed Clinton because he wanted to elect a “sane” person to the White House.