The “vast right-wing conspiracy” is back.

That was the phrase Hillary Clinton herself used to describe the villainous puppet masters behind the Monica Lewinsky scandal back in 1998. And now, her camp has decided to reanimate this ludicrous bogeyman from the days when pets.com was the talk of Wall Street to combat new allegations of Clintonian malfeasance — allegations the substance of which she and we don’t even yet know.

The material dug up by the conservative writer Peter Schweizer for his new book, “Clinton Cash,” is credible enough to have led several news organizations not normally friendly to the right (The New York Times and The Washington Post) to strike deals with Schweizer and his publisher to share and independently substantiate some of its charges.

This a novel arrangement — and the imprimatur of news organizations that liberals like — has clearly frightened the Clintonians in a way past negative books did not.

That explains Clinton press secretary Brian Fallon’s three-page memo seeking to discredit the book before the fact. According to Politico, which obtained a copy, the memo says, “The book was backed by a Koch Brothers-linked organization and a billionaire family that is bankrolling Ted Cruz’s presidential campaign.”

This is a sleazy way to say ­Schweizer runs a group called the Government Accountability Institute, a nonprofit dedicated to exposing corruption. Like all nonprofits, it has donors. Among them are the Mercer family of Long Island, one of whose members threw a cocktail party for Ted Cruz.

It’s also gotten funds from a group called Donors Trust — which, like the Metropolitan Museum of Art and Lincoln Center, receives money from members of the Koch family.

The demonization of the Koch brothers — two libertarians whose involvement in the furtherance of ideas and policies they believe are best for America is anything but a secret — is just the latest manifestation of the tried-and-true tactic America’s liberal politicians and groups employ to send signals to liberal reporters, pundits and activists that the bad guys are on the march against them:

Time to man the barricades. Don’t believe a word they say. Tell all your friends: Nothing to see here. Move along.

In 1998, just a day after she stood beside her husband while he told the public, “I did not have sexual relations with that woman,” Hillary Clinton went on the “Today” show to attack the credibility of the charge by alleging it was the work of “this vast right-wing conspiracy that has been conspiring against my husband since the day he announced for president.”

Of course, Bill Clinton did have an affair with Monica Lewinsky, he did lie about it under oath, he was impeached by Congress (although not convicted), was disbarred and paid a $25,000 fine. But whatever.

It’s always been the Clinton way to deal with attacks by raising questions about the credibility and motives of the attackers while simultaneously pooh-poohing the seriousness of any charge by saying the allegations are old, that there’s nothing new to them.

John Podesta, a senior official in her campaign, said on Charlie Rose’s show on Monday, “The facts: There’s nothing new about the conspiracy theories.”

This, too, is a key Clintonian phrase. Last week, when it was revealed Congress had asked back in 2012 whether Hillary Clinton had a private e-mail system and got no answer, her spokesman Nick Merrill said, “There is nothing new here.”

The database Nexis reveals the first time anyone used the phrase “there’s nothing new here” in relation to the Clintons was on Sept. 20, 1992, in an interview on CNN with candidate Bill’s spokesman, George Stephan­opoulos. Asked whether Bill Clinton sought preferential treatment from his state’s senator when it came to the Vietnam draft, Stephanopoulous answered: “This is an old story. It’s been written time and time and time again and now. It just appears 46 days before the election. But there’s nothing new there.”

The story was true, of course. But so what? In the eyes of the Clintons, it was old, and so didn’t matter. Apparently, if the charge were new, then somehow, it would be more significant than if it were old.

We’ll see if Peter Schweizer has anything new. We’ve already seen we won’t see anything new from the Clintons. For them, sliming an enemy and denying everything have worked for nearly a quarter-century. Like Hillary herself, it’s a golden oldie.