“The Daily Show’s” Jordan Klepper did a horrifying and hilarious series of interviews with the Trump groupies who lined up on Oct. 9, amid Confederate flags and pictures of their hero riding a velociraptor and firing a machine gun, to hear former president Donald Trump speak in Iowa.

A woman in the MAGA hat and U.S. flag overalls denied that Trump supporters are a “cult” while saying, “I feel like whatever he spews out of his mouth, I just love it.” A guy denounced Democrats for “trying to divide [us]” while wearing a T-shirt showing Trump giving the middle finger to President Biden and Vice President Harris. An old-timer in a QAnon shirt insisted that Trump is still president and still in control of the military but denied that he should be blamed for what happened in Afghanistan.

This is appalling and insane. But there has always been a lunatic fringe in U.S. politics. In the 1950s and ’60s, the John Birch Society believed that President Dwight D. Eisenhower was a communist agent and that the fluoridation of water was a communist conspiracy.

It’s true that, thanks to Facebook and Fox “News” Channel, nutty views spread faster and further than in the days when conspiracy theorists had to rely on mailing mimeographed manifestos. But the biggest difference between now and then isn’t the Republican grass roots. It’s the Republican leadership, or lack thereof. In the past, Republican leaders stood up to the zealots in their midst. Today, they stoke the flames of extremism — and wonder why they keep getting burned.

The death last week of Colin L. Powell, the former national security adviser, chairman of the Joint Chiefs of Staff and secretary of state, made me reflect how much we are losing with giants like him departing from the scene. An entire generation of Republican statesmen — men including Powell, George H.W. Bush, George Shultz, Brent Scowcroft and John McCain — regularly put the country’s interests above those of their own party.

Powell, after holding high office under three Republican presidents, endorsed Barack Obama in 2008 and later spoke out against the menace posed by Trump. After Jan. 6, he said he no longer considered himself a Republican and criticized Republicans who “would not stand up and tell the truth.” That earned him, after his death, the ultimate backhanded tribute. Trump, with his trademark cruelty, reviled Powell last week as a “classic RINO.” As for McCain, it has been more than three years since he died, yet Trump is still attacking him and his family. Despite all this, 78 percent of Republicans want this solipsistic sadist to run for president again — and because Senate Republicans refused to convict Trump during his two impeachment trials and bar him from running again, there is nothing to stand in his way.

Where is the next generation of Powells, Bushes, Shultzes, Scowcrofts, McCains? They don’t exist. Those who try to uphold their values — e.g., Sen. Mitt Romney (R-Utah) and Rep. Liz Cheney (R-Wyo.) — are outcasts in their own party. The GOP is now led by unprincipled opportunists, such as House Minority Leader Kevin McCarthy (R-Calif.), who have allowed their party to be captured by the crazies.

My Post colleagues Michael Scherer and Josh Dawsey just revealed how badly McCarthy has compromised principles in the pursuit of power. They report that “McCarthy told one colleague that he would not sign a December amicus brief to a lawsuit from the Texas attorney general seeking to overturn the election ‘because it wasn’t constitutional.’ ” Naturally McCarthy later signed this egregious document. (A McCarthy adviser “contested this account.”)

After the Jan. 6 riot, McCarthy said that Trump “bears responsibility” and should be censured. Yet McCarthy voted against impeaching Trump and went down to Mar-a-Lago to genuflect before the inciter of the insurrection. Not only did McCarthy oppose the creation of a fact-finding commission, but last week he pressured House Republicans not to hold former Trump aide Stephen K. Bannon in criminal contempt of Congress for his refusal to testify about the events of Jan. 6. (Only nine Republicans broke ranks.)

Yet even with his repulsive toadying to Trump, McCarthy may not be the worst offender among Republican elites. It is hard to go lower than Govs. Ron DeSantis of Florida and Greg Abbott of Texas. They seem to be in a sick competition over how many of their own citizens they can kill by catering to anti-scientific prejudices.

Abbott made a strong case that he was the leader in this ghoulish contest by trying to ban all coronavirus vaccine requirements, even in private companies. But DeSantis might have surged back into the lead by appointing as Florida’s surgeon general a fringe physician, Joseph Ladapo, who questions the efficacy of covid vaccines. Last Thursday, DeSantis stood by as Ladapo went down the rabbit hole, complaining about people “being forced to sort of put something in their bodies that we don’t know all there is to know about yet.”

Mock the Republican grass roots all you like. But the real problem is the complete abdication of responsibility by Republican leaders. Rather than trying to restrain the zeal of their most fanatical followers, they are amplifying it. Blame the party’s elites, not its rank and file, for its descent into madness and sedition.