As a former panelist on “Sunday Insight with Charlie Sykes,” now that the New York Times has written about Sykes I guess I can say I knew him when, or more accurately before:

Charlie Sykes, a popular talk radio host here and leader of the “Stop Trump” movement, had spent months hammering Donald J. Trump on his show, calling him a “whiny, thin-skinned bully” and dismissing his supporters as “Trumpkins.”

So Mr. Sykes was surprised when the Trump campaign reached out on Easter Sunday to ask if the billionaire-reality-star-turned-presidential front-runner could come on his show.

The 17-minute interview last week was contentious and combative, with Mr. Sykes pressing Mr. Trump to apologize for comments he has made denigrating women, calling him a 12-year-old playground tormentor, and lamenting that he had failed to introduce the bombastic New Yorker to Wisconsin’s “tradition of civility and decency.”

Later in the week, as Mr. Trump crossed the state, he seemed to acknowledge the power of Wisconsin’s talk radio culture, which has been an anti-Trump force in the state, by railing aloud against it for deceiving voters.

“In certain areas — the city areas — I’m not doing well,” Mr. Trump told voters in Racine, Wis., bemoaning his lack of support on talk radio. “I’m not doing well because nobody knows my message. They were given misinformation.”

Mr. Sykes, along with a handful of other local talk radio hosts, has spent his mornings criticizing and castigating Mr. Trump over the airwaves. And if Mr. Trump loses the Wisconsin primary on Tuesday, he will have Mr. Sykes and his merry band of talkers partly to blame.

In a nominating contest that has exposed fissures in the Republican Party, Wisconsin’s conservative talk radio apparatus remains remarkably united in at least one belief — their deep and utter dislike for Mr. Trump, who for months has been the focus of their fiery attacks.

“Can someone win without talk radio?” asked Mr. Sykes, during a commercial break from his show. “Yes, theoretically. Except no one has.”

Wisconsin’s conservative talk radio has long played an outsize role in a state whose position in the Republican primary calendar has now given it heightened status in the nominating process.

When Mr. Walker, who ended his own presidential bid earlier this year by offering a pointed rebuke of Mr. Trump, endorsed Senator Ted Cruz on Tuesday, he did so by calling into Mr. Sykes’s show. And the week before, Mr. Cruz kicked off his Wisconsin primary bid in a friendly interview with Mr. Sykes.

Mr. Trump, by contrast, has found himself under near constant fire from the conservative talk radio hosts that dominate the southern part of the state, including the three counties that include parts of Milwaukee — Waukesha, Ozaukee and Washington — that are among the most conservative in Wisconsin, and where Mr. Trump is struggling the most.

The most popular conservative talk show hosts here — Mr. Sykes, Jeff Wagner of WTMJ, and Mark Belling, Vicki McKenna and Jay Weber of WISN — are united in their disdain for Mr. Trump, with Jerry Bader, a radio personality at WTAQ in Green Bay, rounding out the group.

“The thing that’s been unique in this presidential race is, for some reason, the three who work here — Jay, Vicki and myself — and our competitors, Charlie and Jeff Wagner, all seem to despise Trump,” Mr. Belling said in an interview. “We all just kind of came to this conclusion independently. I think it’s just that we’re not as stupid as some of the people that are falling for Trump’s crap.”

In Mr. Belling, Mr. Trump has found an antagonist who is just as bellicose as the real estate billionaire himself. In his broadcast on Monday, Mr. Belling called Mr. Trump “the biggest wussy of all time,” “a big crybaby,” and a “sissy,” before turning his attention to the campaign team and declaring: “His staff are probably just a bunch of butt kissers.”

And that was just in the first hour.

“It seems to me that if you are an intelligent, thinking conservative who cares about issues, you’d be mortified that this moderate loudmouth boor would be hijacking a movement that you cared about,” Mr. Belling said, later, in an interview.

Nonetheless, on Monday, Mr. Trump made a round of calls to the state’s local radio hosts. The series of interviews, contentious and combative, did not go particularly well.

Ms. McKenna challenged his promise to build at wall at the nation’s southern border — “What does it look like? Where does it go?” she pressed him — and urged him to declare “wives and kids off-limits,” after Mr. Trump’s public spatinvolving pictures of his wife, Melania, and of Heidi Cruz, Ted Cruz’s wife.

Yet despite Ms. McKenna’s pleas that Mr. Trump “unify” the party, the interview ended on a rough note, with Mr. Trump hanging up on her.

Mr. Bader, the host in Green Bay, began his interview with Mr. Trump bluntly as well. “I have some concerns about both your behavior and what I consider to be vague policy positions,” he said.

In an interview, Mr. Bader described his conversation with Mr. Trump as “feeling like a ‘Saturday Night Live’ skit.” “Like this isn’t real,” he said. “And to me that’s what his entire campaign feels like.”

That Mr. Trump, who has singled out reporters he does not like and banned certain media outlets he deems critical from attending his events, has pandered to the talk radio crowd here not only highlights the group’s clout, but also may reveal a general election calculation.

“The last thing you want to do as a Republican is irritate your base as you go into a general election in a swing state like Wisconsin,” said Mark Graul, a Republican strategist who ran George W. Bush’s campaign in Wisconsin in 2004 and has run other statewide races since. “And in many ways, talk radio is the voice of base Republicans in Wisconsin.”

The Wisconsin electorate, which gave rise to Speaker Paul D. Ryan — a hometown congressman whose attraction is predicated on civil discourse and serious policy proposals — is particularly well primed for the talk radio pitch here, which appeals to both their sense of conservative principles, as well as their Wisconsin-nice demeanor.

“For whatever reason, there is a pragmatism to Wisconsin hosts that you don’t see en masse in a lot of other hosts,” Mr. Bader said. “I believe I have a moral responsibility to do whatever small part I can in stopping Donald Trump. It’s beyond politics for me. I think he’s dangerous.”

And from Mr. Sykes: “I think talk radio has been more substantive, more intellectually serious here and therefore less prone to embrace an entertainer.”

“I feel very strongly that Donald Trump poses a fundamental challenge to the conservative movement, an existential challenge, so yes, I have made it my mission to stop him,” Mr. Sykes added.

Sykes’ next to last quote is a bit ironic given that the godfather of conservative talk, Rush Limbaugh, makes no bones about being an entertainer. People tend to forget that radio is a business, and if your ratings aren’t good enough, you are a poor advertiser draw, and then out the door you will go. But given how long these six have been on the air, clearly their shows work. (As opposed to liberal talk radio, which keeps getting tried and keeps failing, with few exceptions like Sly and 92.1 in Madison.)

I don’t listen to any of the six regularly anymore since their signals don’t get as far southwest as I am, and I don’t listen to them online because I work when they’re on the air. My past impression is that at least some of them, including Sykes, are avid boosters of Gov. Scott Walker specifically (in Sykes’ case going back to Walker’s Assembly days), and when I was a more regular listener I didn’t hear a lot of criticism of Walker. That could be part of their motivation for their Trump distaste, although all six were here during the heyday (if you want to call it that) of Act 10 and Recallorama, and Trump wasn’t.

Sykes, on the other hand, is the inspiration of what has been called the “Sykes effect,” over positions favored by Sykes that might be at odds with GOP leadership. (The “Sykes effect” isn’t found where I live, where neither Sykes nor any other Wisconsin-based conservative talk radio exists.)

The thing about what Sykes, Wagner, Belling, McKenna, Weber and Bader do, however, is that listeners are free to listen, or not.