As we have learnt in Charlottesville, Pittsburgh and Orlando, hate is not about geography.

The Clark brothers grew up in a dynamic and diverse neighbourhood in the nation’s capital, on a street with American flags and rainbow pride flags, pick-up trucks and Vespas.

Their neighbours included elderly African-American porch sitters, working-class Latino families and, increasingly, affluent young couples walking overbred little dogs.

But inside that home, where the brothers lived with their sister and father, they existed in an alternate universe.

They had boxes of ammunition and gun parts, nooses hanging from the ceiling, at least four weapons and Nazi flags, according to a police affidavit filed last week in the United States District Court in Washington.

There was the constant smell of cannabis, plus a whole growing operation, the kind of blow torches meth smokers use, and hours’ worth of violent, racist video games. Ethnic Cleansing was their favourite, the affidavit said.

They visited alt-right events, investigators said, and openly talked about a coming race war.

“Get used to it, libtards. This is just a dry run for things to come,” one of them is accused of posting online, after pipe bombs were sent to prominent critics of Donald Trump, including Barack Obama, the former president.

“According to [two relatives], Jeffrey and Edward Clark believed that there would be a race revolution, and they wanted to expedite it,” the affidavit states.

Accused white nationalist warriors who lived in plain sight, the Clark brothers apparently became radicalised online, in the multicultural heart of one of America’s most politically liberal cities.

No broken-down factories, rural blight, dead farms, decrepit schools, trucks or coalmines needed, y’all.

That is one of the myths about America’s divisions.

White male resentment that decays into racial hatred cannot be pegged simply to economic hardship or unemployment or the growing diversity of America.

When the Clarks moved to their street more than a decade ago, they were among the first white families to buy there. Their gentrifying neighbourhood in northwest Washington — a place of charming, turn-of-the-century terraced houses and hipster restaurants two miles from the Capitol — became richer and whiter.

Their townhouse doubled in value and is now worth nearly $1 million, real estate records show. The area was moving in the direction that their hate groups like. So what made the Clark brothers, according to police, talk openly about “killing Jews and black people”?

Enter the dark underworld of online hatred. All you need is wi-fi.

This is how the police got involved with the Clark brothers.

The older brother — Jeffrey “Raph” Clark, 30 — was arrested in the District and remains in custody after family members flagged his erratic behaviour, violent threats and social-media connection to Robert Bowers, the man in jail after being accused of the massacre in a Pittsburgh synagogue last month.

Jeffrey’s handle on Gab, a preferred social-media platform for bigots, is @PureWhiteEvil, and he describes himself as a “meth-smoking, pipe bomb making, mailman-murdering” member.

In their house, investigators found, among the nooses, ammo, armoured vests, pot plants and Nazi flyers, a sketch of someone with a gun aimed at the head of a bearded man wearing a yarmulke, along with scrawled talking points, including: “Legalise Discrimination. Cut off all welfare. Deport all illegal immigrants. End birthright citizenship.”

Just a couple of hours after that horrific Pittsburgh shooting, the younger brother — Edward “Teddy” Clark, 23 — left the house with a loaded Beretta pistol and two extra magazines full of ammo.

Family members “believe he may have been planning to commit an act of violence”, the affidavit said.

Instead, three hours after 11 people were killed in Pittsburgh, Teddy crossed the Potomac River to Roosevelt Island and killed himself.

When relatives came in to deal with Teddy’s death by suicide, they found an older brother who was “really riled up” and “agitated”. Jeffrey was defending the synagogue massacre, investigators said.

On Gab, he called Bowers a hero and said, of those killed, that “every last one of them deserved exactly what happened to them and so much worse”, according to court documents.

So the family called police, and he was arrested on weapons charges. On Friday, a federal judge denied him bail.

We will never know whether the Clark brothers were really planning a massacre of their own.

But until the family called, they were nowhere on anyone’s radar, 2½ miles away from FBI headquarters.

This is one argument for red-flag laws, which allow family members, law enforcement officials and healthcare workers — even co-workers, in some states — to petition the court for a temporary removal of weapons from someone who may be suicidal.

“The people who know people best are family members,” said Liza Gold, a clinical professor of psychiatry at Georgetown University Medical Centre. “And they are often the ones who recognise when someone is getting into a dangerous place.”

The Clark brothers show us that the dangerous place can be anywhere.

It’s easy to pin the growing white-power movement on a Confederate flag-loving, good ol’ boy relic of the South. Or a reaction to white America’s Rust Belt woes. But hate such as this cannot be about zip codes.

Charlottesville, the liberal-leaning university town at the centre of the deadly Unite the Right rally last year, is also the home town of its white nationalist organiser, Jason Kessler.

The Pittsburgh neighbourhood where the synagogue massacre happened is the home town of Mr Rogers and a diverse, liberal enclave.

And Washington, where there has been an explosion of white prosperity and wealth throughout most of the Clark brothers’ lives, and which voted 90 per cent for Hillary Clinton in 2016, hardly seems like the place to fly a Nazi flag. But the Nazi flag was there. On the inside.

• Petula Dvorak is a columnist for The Washington Post’s local team who writes about homeless shelters, gun control, high heels, high school choirs, the politics of parenting, jails, abortion clinics, mayors, modern families, strip clubs and gas prices, among other things. Before joining the Post, she covered social issues, crime and courts