The malady known as Trump Derangement Syndrome is marked by a sudden explosion of crazy talk and sometimes actions coming from people formerly regarded as sane. Its sufferers, most, but not all, living on the left wing of the political spectrum, are prone to declare Donald Trump an existential threat to everything, and therefore feel entitled to fight fire with fire.

Think of the threats of impeachment before Trump was even inaugurated. Or the fantasies of unhinged celebrities such as Kathy Griffin, Robert De Niro and Madonna that the president or his family suffer violence and maybe death.

All this reprehensible conduct was winked at by the national media because Trump is obviously such a bad, bad person. He is so bad that he had managed to drive good people crazy, so who could blame them?

Yet now, two years into a Trump presidency, a new malady is emerging, one that reflects a less hostile view of him. It is an implicit recognition that the most unlikely commander-in-chief has not only survived, but is thriving in some ways.

I think of this new disease as Trump Imitation Syndrome because its sufferers are behaving in ways that are downright Trumpian.

New Yorkers — aren’t we lucky? — are getting a double-dose of it, courtesy of Gov. Andrew Cuomo and Mayor Bill de Blasio. Both are Democrats and both made vicious attacks on Trump a main feature of their successful re-election campaigns. But because imitation is indeed the sincerest form of flattery, we can assume they now see political virtue in Trump’s method.

The governor, stung by criticism of the enormous subsidies and power grab he used to lure Amazon to Queens, is turning on much of the media with a ferocity straight out of the president’s playbook.

Cuomo, in a statement that his office dubbed an op-ed, although it had not been published anywhere else, took a blowtorch to The Post, The New York Times and CNN. He accused all three of being hypocrites because they, too, had received tax credits or other benefits for job creation and retention in the past.

“This transaction is a lightning rod for the political rhetoric on both extremes,” Cuomo wrote, saying, “Extreme conservatives and the socialists both now vehemently oppose ‘incentives’ for Amazon.”

He suggested that antagonism toward the deal was driven in part by the fact that Amazon’s Jeff Bezos also owns The Washington Post, and is thus a competitor of the media critics.

The governor didn’t use the words “fake news,” but he might have, for he was copying you-know-who in trying to discredit criticism as being driven by hidden agendas and personal ambitions.

To underscore the point, Cuomo issued a second blistering attack after the Times hit him in another editorial.

The comparison will be complete if he can find a version of Jim Acosta to slap around.

Then there’s Mayor Putz. His own 2017 campaign featured so much presidential bashing that one left-wing outlet credited him with teaching “Democrats How to Fight Trump” and another said he “Finds His Mojo as the Anti-Trump.”

That was then. But last Friday, while New Yorkers were still recovering from a disastrous City Hall response to a 6-inch snowstorm, the mayor fired the head of the Department of Investigation, the city’s chief watchdog.

The official, Mark Peters, formerly a close friend and ally, fought back, accusing de Blasio of trying to quash investigations that revealed wrongdoing in his administration.

Echoes of James Comey’s charges against Trump after he was fired are unmistakable. Indeed, Peters issued a long letter to the City Council, alleging that a deputy mayor asked him to kill an investigation and that when he declined, he was told he was not being “loyal” and was no longer “a friend” of the administration.

A demand for loyalty — that rings a bell. Oh, right, it was a heinous crime when Trump supposedly did it. Now, everybody does it, ho hum.

And imagine if Trump fired special counsel Robert Mueller — what would de Blasio say?

National Democrats, despite their loathing of all things Trump, also play the imitation game. The penchant among Dem losers in Florida, Georgia and elsewhere to declare elections rigged because they lost are examples of how they have adopted traits they denounced in Trump.

The president is no doubt flattered by the unspoken tribute coming from copycats. By adopting his ways and style, they clearly hope to copy his success.

But they won’t. Trump’s success came in large measure precisely because he wasn’t copying anybody — he was being uniquely himself.

There was nobody like him in either party. Recall how Sen. Marco Rubio, once thought to have a good chance at the GOP nomination, panicked as his chances slipped away and decided to get into an insult contest with Trump.

Few people remember what exactly he said to the front-runner, but nobody will forget that Trump dubbed him “Little Marco.” End of contest.

Or recall one of the greatest knocks voters had on Hillary Clinton — she was inauthentic. Like a chameleon, she changed colors depending on the audience.

The message is clear: Knockoffs should beware. There is only one Trump.

Families face divisive holidays

Thanksgiving is a great, uniquely American holiday, with the modern mix of family, food and football capturing something fundamental about our remarkable nation.

Yet amidst the love comes the realization that deep divisions are tearing us apart. While many families will avoid politics Thursday, those who dare to wade in might use as a starting point a chilling letter from reader Carole Campolo. She writes:

“Today we commemorated our beloved veterans, many of whom gave their lives to protect our country from foreign enemies, but I believe the real threat is coming from within.

“Antifa mobs attack individuals and their families without anyone being held to account, deep staters use the power of their office to try to take down an administration with whom they disagree and there is demonization of Trump supporters.

“I believe our country has gone over the edge and only a miracle or unfortunately some catastrophic event can bring us back together.

“There are so many of us out here who are devastated and feel helpless to change the negative trajectory of our beloved country. Our votes are being nullified, we are being called Klan members and we believe it is only a matter of time before we too will be attacked physically if we are too verbal about our beliefs.”

Air travelers in a real fix

From the Daily Mail: “Passengers are forced to chip in to pay for REPAIRS to their Boeing 787 before it takes off from Beijing to Poland.”

And you thought air travel couldn’t get worse.

A stock tip that’s no bull

Word to the wise.

With once-high-flying tech stocks coming back to earth with a thud, Wall Street strategist Bruce Bittles offers a warning to investors that could apply to most things at most times.

He tells The Post: “When things get too popular, be careful.”