Charles Perretti and the North Country Peace Group were on to their Mercer neighbors from near the beginning.

Today, Long Island’s Mercer family defines a key aspect of the national landscape. They spent millions backing President Donald Trump when others wouldn’t.

But in 2014, Robert Mercer was mostly known as chief executive at storied hedge fund Renaissance Technologies, which the Senate concluded had failed to pay more than $6 billion in taxes.

This rankled Perretti, 72, a marine biologist turned retired Northport educator who speaks of civic affairs in hushed, intense tones. He’s the kind of guy who worries about non-soy-based inks and post-Citizens United plutocrats hurting democracy, like Mercer at Renaissance. And where was this company located?

“My God,” Perretti remembers thinking. “It’s right up the block.”

Steps, that is, from the corner of Route 25A and Bennetts Road in East Setauket, where the North Country Peace Group says it has met or held protests every Saturday for some 15 years. Down 25A is Renaissance, where Mercer earned the money for his investments in outfits like Breitbart News, which has muddied political discourse for years. Money that also went to the data firm Cambridge Analytica, facing scrutiny from congressional investigators looking into potential collusion between Russia and Trump’s campaign, and to help elect Trump. The source was nearby, but in terms of political influence, the little peace group was light-years away.

The peace group started as a band of Christians and humanists protesting the Iraq War, and grew to include retired doctors and graduate students from the Three Village area, home to Stony Brook University. There they stood or sat, in the cold, discussing the news, 30 strong or just a handful, making their voices heard on nuclear weapons, closing Guantánamo’s prison, supporting Colin Kaepernick.

“It’s got a lot of advantages,” Perretti says of the corner — good cross-traffic, spots where you can “intercede” with drivers. With the Mercers, the core problems the peace group saw in the world might never be closer. So in 2015, they began to plan.

They marched up to Renaissance’s offices on 25A, carrying signs saying, “Keep corporate $ out of politics,” and posing next to the lightly marked complex entrance: a big parking lot, an American flag. They presented a letter asking the businessman for a meeting. This didn’t immediately work, but at another demonstration before the 2016 New York presidential primary, group members talked to Renaissance employees about the political implications of Mercer donations. Then, they got a response: an email from a Renaissance staffer to Perretti. In it, Mercer asked Perretti to dinner.

“I was flabbergasted,” Perretti said recently. “I never thought he would acknowledge us. We were a flea on the elephant.” They’d had reactions from past protests — kind words from supporters vs. coffees thrown from passing cars. But here was something big, the promise to learn about the figure down the road.

It’s only in recent years that Mercer and his family have come into wider view. (Repeated efforts to reach the Mercers for comment were unsuccessful.)

Former Rep. Tim Bishop, the Democrat who lost his Long Island congressional seat to Mercer-funded Lee Zeldin in 2014, recalled a story Oregon Rep. Peter DeFazio told him in 2010 about a guy in Bishop’s district funding DeFazio’s opponent. “That’s how I learned that Robert Mercer existed,” Bishop said recently. DeFazio had proposed a tax that might have cut into Renaissance’s margins, and his opponent was a Mercer-favored climate-change-denying scientist.

In the flood of media profiles about the Mercers are the same stray libertarian-leaning details: the intricate $2.7 million train set on Mercer’s estate, its cost revealed in court records after the likely billionaire sued the train maker for overcharging (his exact wealth is hazy, but the hedge fund is estimated to be worth billions). There’s the origin myth of his computer work before arriving on Long Island to join founder (and cross-aisle donor) James Simons at Renaissance: Mercer got fed up with what he saw as government waste while doing collegiate work on an Albuquerque military base. That’s from a rare public speech in 2014. The peace group was excited about its surprise chance to learn more.

Perretti sent a return email to Mercer via the staffer asking if they could meet on more neutral turf: at a Setauket diner. As a scientist, he also asked pointedly if they “both agree that our planet is experiencing an accelerated rate of CO2 atmospheric saturation with the probability of significant heat build up in the air and oceans?”

But the staffer wrote back with replies from Mercer. “I enjoy discussing issues at dinner,” Mercer wrote. “I enjoy eating dinner at my house.”

As per the diner: “I do not enjoy eating at restaurants because I do not hear well in that type of environment.”

And on the global warming question: “It is likely that we do not agree on this.”

Perretti considered the situation and decided not to meet with Mercer on his terms. It did not seem a promising way to start a productive conversation. Another member of the group took the plunge, but wasn’t rewarded much for the meeting, which was wrapped in a nondisclosure agreement. Mercer likes his privacy.

These interactions didn’t develop into the kind of dialogue the peace group had wished. Since their emails, Perretti hasn’t heard from Mercer, but the donor only grew in prominence after he and his daughter Rebekah switched allegiances from Texas Sen. Ted Cruz to Trump in 2016.

When Trump won, Rebekah became a member of the transition team. Trump attended the annual Mercer costume ball at Owl’s Nest, the family’s Head of the Harbor estate. The party theme was “villains and heroes.” The year before it had been World War II, and a tank watched the entrance. But the Mercers’ hidden halls and their luxury yacht have long been guarded locations for conclaves that are rarely glimpsed yet have profound impact for hashing out political strategy or campaign plans.

For that reason, the peace group didn’t give up. Members have protested along 25A, dressing in puppet costumes to highlight the idea that campaign contributions come with strings attached. Others gathered not far from their usual corner outside Owl’s Nest, where they glimpsed the owl sculptures framing the gate. They tried to learn more about the family, even talking to a suspended Renaissance employee who wrote an op-ed in The Philadelphia Inquirer about how Mercer “now owns a sizable share of the United States Presidency.”

This troubled the group. Its members are still not exactly sure what motivates the family next door. The Mercers’ actions are not always linear, and sometimes can surprise. But there are few checks on their money-bought influence, whenever they decide to do what they want to do.

And that might be the most troubling piece of all.

Mark Chiusano is a member of Newsday’s editorial board.