For generations, the Horowitz family has cheered on the revolution.

Phil and Blanche were New York schoolteachers who belonged to the Communist Party, and dreamed of a socialist heaven on earth. Their son, David, went on his first march in 1948, at age 9. As a young man in the 1960s he helped create the New Left, which pushed for the rights of the oppressed and struggled to end the Vietnam War. David worked closely with the Black Panthers, who believed a violent uprising was at hand and they would help lead it.

David’s youngest son, Ben, sought his fortune in Silicon Valley, a generally liberal place that traces some of its roots to the rebellious spirit of the ’60s. Ben became a leading venture capitalist, investing billions of dollars in start-ups like Twitter and Facebook that seek to topple the status quo. His firm’s investment thesis is “software is eating the world” — as disruptive a vision of the future as the old Marxist dream of the state withering away.

And now David, after a political odyssey that took him from the extreme left to the extreme right, has a surprise last act that puts him once again in the thick of insurrection. His radical views on immigration, race, education, the duplicity of the media and the treachery of liberals have abruptly made their way to the center of power. If the Trump administration has an intellectual godfather, it’s David Horowitz.

Father and son are a snapshot of America at this moment, a politicized and polarized place full of competing revolutions. They live in different universes: one where President Trump is the answer, the other where he is the problem.

During Jeff Sessions’ confirmation hearings as attorney general in January, Democrats raised the issue of the long and admiring relationship between David and the nominee. Statements by David like “too many blacks are in prison because too many blacks commit crimes” were cited as evidence that Mr. Sessions kept unsavory company and had racist leanings.

A few weeks later, Ben gave a talk on “How to Start a Cultural Revolution” at a Silicon Valley conference. Wearing a T-shirt emblazoned with a picture of Toussaint L’Ouverture, the Haitian who led a slave revolt two centuries ago, Ben took his audience through the details of L’Ouverture’s unlikely success and what they could learn from it.

Blacks as criminals, blacks as role models — it’s hard to get further apart than this. Yet for a country that seems riven in two, the Horowitzes offer a measure of hope. They email, they talk, they get together for family celebrations. When David went to college campuses to denounce things that Ben believes in, Ben paid for his bodyguard.

To understand all might not be to forgive all, but it’s a start. David and Ben both said they have made a major effort to see where the other is coming from. While no one’s politics have changed, they realized they are not quite as far apart as it might seem.

“One thing we mostly see eye-to-eye on is that the most important thing is the ability of an individual to live his life and have an opportunity,” said Ben, 51. “How he went from ‘The way to do that is Communism’ to ‘The way to do that is Trump’ is amazing.” He laughed. “That’s where we’re not aligned.”

David said he is glad he never foisted his beliefs on Ben or his other children the way Phil and Blanche’s relentless adherence to the Communist doctrine pushed David into the cause long ago. If the revolution has a few less soldiers this way, so be it.

“I’ve come to the end of the story,” said David, 78. “I don’t mistake the life I’ve lived for the only life.”

It’s not that simple, of course.

“Sometimes people try to connect us on Twitter, which is always scary,” said Ben. “Someone will say, ‘Hey, aren’t you related to @horowitz39?'” That’s David’s handle on Twitter, where he says things like “Obama is an American traitor” and “Hillary killed four Americans in Benghazi.”

“I never reply,” Ben said.

In the horse country northwest of Los Angeles, it’s a glorious day. David Horowitz and his fourth wife, April, live here inside a remote gated community. There are two horses and, making a terrible racket, several dogs. Gardeners are working on the lawn.

“Don’t ask me if they’re illegal,” David said with a laugh.

The house is only remote physically. The computer in the other room is always calling, bringing forth updates, denunciations, the ongoing political spectacle. “How can you feel isolated when you’re connected all the time?” David asked.

He chronicled his family’s penchant for revolution in his 1997 autobiography, “Radical Son,” one of the most prominent of a long shelf of volumes. His first effort, “Student,” about the embryonic turmoil on college campuses, appeared when Kennedy was president. In 1968, he became an editor and writer for Ramparts, the radical magazine that nurtured and reflected the era’s unrest.

“The system cannot be revitalized; it must be overthrown. As humanely as possible, but by any means necessary,” Ramparts proclaimed in a 1970 editorial. David says he was the one who insisted on adding the “humanely” part.

Ramparts published Che Guevara’s diaries, went after the C.I.A. and offered a tutorial on how not to pay taxes. Its international editor was Black Panther leader Eldridge Cleaver, who fled to Cuba in 1968 after leading an ambush of Oakland, Calif., police officers. Thanks in a large part to Ramparts, the charismatic and photogenic Panthers soon embodied the notion of revolution for white radicals.

David found a political soul mate in Panther leader Huey Newton. He immersed himself in the Panthers’ home base of Oakland, raising money to buy a 35-classroom school that would be a showcase for the cause. Even for that freewheeling era, Ben had an unusual boyhood. It would shape his life, friendships, marriage and work. His best friend, who would later be best man at his wedding, was black. He was one of the few white kids on the Berkeley High football team. Every Sunday, he went to the Son of Man Temple, the Black Panther church in the auditorium of the school.

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“I know all the songs from there,” Ben said, and as proof, started singing the old gospel hymn adopted by the Panthers, “We are soldiers in the army …”

David said: “Ben is practically black.”

Ben laughed when this was repeated to him, something he does frequently when talking about his father. “I hate it when my father talks, it’s ridiculous,” he said. But he acknowledged its broad truth.

In the Bay Area in the early 1970s, the revolution seemed at hand. Marcus Foster, Oakland’s first black superintendent of schools, was assassinated in November 1973. Three months later, Patty Hearst was kidnapped in Berkeley. In August 1974, Mr. Newton was arrested after the shooting of a prostitute and fled to Cuba.

When the Panthers needed someone to keep their finances, David recommended a white friend named Betty Van Patter. In late 1974, she disappeared. A few weeks later, her body was found in San Francisco Bay. Her head had been bashed. While the murder was never officially solved, David held the Panthers responsible and said Mr. Newton confirmed it years later.

The person he really blamed, however, was himself. The Panthers, he concluded, were thugs dressed up as revolutionaries, but the Left was too wrapped up in its dreams to be honest about it. David became unglued. He bought a sporty Datsun 260Z, had an affair, divorced his wife Elissa after nearly two decades of marriage and barely escaped with his life when a train smashed up the car.

A photo from this era shows Ben and his two sisters perched with their father on the Datsun. David stares at the camera. Ben looks at the ground, morose.

“I was a very sensitive kid, supersensitive,” Ben said. “He was loud and intense. Which is why I ended up spending so much time with my mom.” (Elissa Horowitz declined to be interviewed for this story.)

In 1976, David wrote with his friend Peter Collier his most popular book, a history of the Rockefeller family. Phil Horowitz, a believer to the end, asked his son why he wasn’t writing about the revolution instead.

“There is no revolution coming,” David angrily replied.

By 1984, he was voting for Ronald Reagan.

Like the sons of many prominent fathers, Ben spent a long time trying both to understand and escape his father. He studied computer science, a subject his father had no interest in, at Columbia University and then the University of California, Los Angeles. In 1990, a connection of David’s helped Ben get an interview at SGI, a pioneering computer graphics company.

Even the tech world, a place that celebrates straight-talking, found Ben a little too direct. “Every now and then, I had to help him better understand how to navigate,” said Ken Coleman, his SGI mentor and one of the few black executives in the tech industry. SGI managers actually had a meeting about firing Ben but did not go through with it.

After SGI came Netscape, the iconic internet browser company. It was here that Ben first acquired a reputation as a manager.

“In Silicon Valley, people always say that an extroverted engineer is one who stares at your shoes rather than his own,” said Greg Sands, a Netscape colleague. “Ben was an engineer, which meant he had a bit of an awkward user interface, but perhaps his life as an outsider generated empathy. He could get people to work together.”

At Netscape, Ben met his future business partner, Marc Andreessen. They went on to start a data storage company called Loudcloud, which had many near-death experiences before it was successfully sold to Hewlett-Packard for $1.6 billion in 2007.

As Ben became more successful, he eclipsed his father.

David spent much of his energy attacking universities, which he considered hotbeds of misguided leftist thought. During one campus visit, he did a radio interview where the host made a personal observation about David that he considered untrue; he doesn’t remember what. Lies deserve lies, he figured, and immediately blasted back: “At least I’m not a child molester like you.”

Ben heard this story from the bodyguard, who was ferrying David as the phone interview was taking place. “I nearly crashed the car,” he said.

David was unrepentant: “You gotta fight fire with fire.”

In 2009, Ben and Mr. Andreessen formed their venture capital firm, which today has $6 billion under management. By then, Ben had managed to tone himself down.

“With my father, everything was an argument to the death,” he said. “My bar for ‘inflammatory’ was so high.”

David declined to follow suit and moderate his own rhetoric, which meant he was largely ignored by both the right and the left. By 2012, the Jewish magazine Tablet could run a profile with the headline, “David Horowitz Is Homeless.” “I’ve been ghettoized,” he told the magazine.

Then came Mr. Trump. When Jeff Sessions was a Republican senator from Alabama, he participated several times in events at the David Horowitz Freedom Center, which describes itself as combating “the efforts of the radical left and its Islamist allies to destroy American values and disarm this country.”

Three years ago, Mr. Sessions got an award from the center. Stephen Miller, a top White House aide, has been relying on David for advice since he was a student battling the administrators at Santa Monica High School.

Last October, Chris Ruddy, a good friend of Mr. Trump’s, commissioned David to write a book about how the right could mobilize to defeat President Clinton. It was taken as a given that she would win the election.

The plan was to publish the book a few days before her inauguration. David began with a section called “The Adversary.” Hillary, of course.

“I can do that almost in my sleep,” he said.

When Trump surprised the world by winning, the book was quickly retooled into “Big Agenda: President Trump’s Plan to Save America,” although much of it was still about how Mrs. Clinton and Democrats were the adversaries. “The strategy,” David wrote, “is to go for the jugular.” The book was on The New York Times nonfiction best-seller list for 11 weeks.

“What I like about Trump is he’s not your typical Republican,” David said. “He’s a fighter.”

A fighter, as it happens, in the style of David Horowitz. In decades of public speaking, David honed an in-your-face approach. He said he picked it up from his former comrades on the left.

“If you’re nuanced and you speak in what I would call an intellectual manner, you get eaten alive,” he said. “It’s a great handicap to be talking like accountants while the opposition are making moral indictments.”

Having politics so deeply part of your identity used to be unusual, said Daniel Oppenheimer, who wrote “Exit Right: The People Who Left the Left and Reshaped the American Century” about David Horowitz, Ronald Reagan and a few others. The core identity of most people was community, family and religion. But as these other parts of society withered, politics filled the void.

“There’s a sense in which we’re all David Horowitz now,” said Mr. Oppenheimer. “We’re all amateur political pundits, and we’re all less willing to compromise. That doesn’t bode well for our future.”

Sand Hill Road is the short, architecturally undistinguished strip just west of Palo Alto, Calif., where the venture capitalists hang out. As an incubator of revolutions, Sand Hill has had a longer and more successful run than Berkeley ever did in the 1960s. Companies from Amazon to Google were funded here.

Tech companies, international in outlook, sales and employment, have little in common with President Trump’s nativist impulses. Mr. Andreessen, the more histrionic side of Andreessen Horowitz, recently said the tech community is so “extremely left-wing, extremely liberal” that a lot of people there could not even articulate a case for Mr. Trump, much less agree with it.

Mr. Andreessen, as it happened, did not want Ben to articulate a case for his Trump-supporting father. “Marc said, ‘Don’t do it, don’t do it, don’t do it,'” Ben recalled.

But his father asked him, and so there was Ben on a couch in his Sand Hill office, mulling the unexpected confluence of race, politics and technology that is the Horowitz family. In case of trouble, an aide recorded the conversation.

“Marx said, sharpen the contradictions. He was talking about the contradictions between labor and capital. Make it stark,” Ben said. “My father, from a rhetorical, propaganda kind of messaging school, is all Marx and Lenin, still.”

In other words, he goes to extremes.

Father and son usually avoid politics, discuss it when they must, and find common ground to the extent they can. They live with each other’s extremes, especially with regard to race.

“We trust each other’s intentions,” Ben said.

For more than 25 years, Ben has been married to Felicia Wiley, who is black and grew up in a working class family in Los Angeles. She is a frequent volunteer at Glide Memorial Church, the longtime countercultural rallying point in San Francisco that talks on its website about how it offered “a safe space” to the Black Panthers. Last summer, Glide gave Felicia a major award.

Ben and Felicia have three grown children. In David’s 2016 essay collection “Progressive Racism,” he wrote, “I have three black granddaughters for whom I want the absolute best that this life and this society have to offer.” But his positions on racial issues are not exactly mainstream in liberal Silicon Valley. In “Big Agenda,” he called Black Lives Matter a “racist” and “riot-fomenting” organization.

And in lines that emphasize how far he had come from the idealism of the 1960s, he wrote in “Progressive Racism” that “there will always be racists and bigots. Only utopians will fail to understand this and seek to deploy the coercive powers of the state to make everyone believe as they do.”

Ben looks at his father’s racial statements in this light: “He’s trying to help black people. Really, genuinely. Nobody else is going to take it that way because of how he says it.”

He noted that his father broke with right-wing orthodoxy and condemned George Zimmerman for the killing of Trayvon Martin. “A young man who was unarmed and guiltless of any crime is dead,” David wrote in 2013. “And shouldn’t there be some penalty to pay for that?”

Ben was one of the speakers at David’s 75th birthday celebration at the David Horowitz Freedom Center. The son said his father “has a nose for freedom and is absolutely relentless about pursuing it,” and announced that he and Felicia were giving the center a $25,000 donation.

Racial questions sometimes come at Ben from other directions. At Andreessen Horowitz, nine of the 135 employees are black. “People say, ‘What are you doing?'” said Ben. The question comes up because the situation is so rare: Only about one percent of the tech workers in the Bay Area are black.

“Those are the people I’m comfortable around,” Ben said. “It’s weird my father was the origin of it, given who he is now.”

Growing up in black culture, Ben developed a love for hip-hop music and used its lyrics as epigraphs for his blog posts on management. An article documenting his affection for the music came to the attention of Divine, a rapper who spent a decade in prison for selling drugs.

“I was skeptical,” said Divine, who was born Victor D. Lombard. “I thought it was a publicity stunt. I couldn’t tie together an older white gentleman who was a venture capitalist and a billionaire to hip-hop, which comes from poverty, from struggle, from pain.” He reached out to Ben via Twitter, realized his sincerity, and the two became friends.

Divine has met David at Ben’s parties and has pondered what separates and joins the two.

“It’s like Ben is the antidote to David Horowitz,” he said. “He balances his father out. And what’s so crazy is that Ben came from David Horowitz.”

In the same way a Mafia don is happy if his kids never whack anyone, David appreciates how his offspring stayed clear of the family business. He doesn’t even mind the way they rejected his politics as well.

“The victory of not indoctrinating your kids and yet having them be successful anyway — that’s the ultimate for him,” Ben said.

Because really, who in their right mind would choose to be involved in politics now?

“I liked it when there were fringes on the left and the right and a somewhat rational center,” David said. “We’ve lost the center. Normal people are wary of politics, with good reason. It’s a very dirty business.”

If David himself were to renounce that business, declaring that his benevolent attitude toward his family would now be extended to strangers as well, this would be a tidier and more hopeful story.

The odds are higher that Hillary Clinton will get an award from the David Horowitz Freedom Center. Despite his distaste for politics, David can’t afford to retire and wouldn’t want to anyway.

“It would be like dying,” he said. “I can’t betray my cause.”