On a leafy street in America’s richest county Jessica Mendez, a mother-of -two, was on her doorstep telling a TV crew why she opposes critical race theory.

As she did so, her female neighbour walked by, and raised both middle fingers in the air.

"I’m really hurt right now," Ms Mendez said tearfully. "I thought that we had a rapport, that I could be conservative and she could be liberal, and we could still be friends. I guess I was wrong."

The incident summed up the toxic atmosphere that has overtaken the genteel environs of Loudoun County, Virginia, on the outskirts of Washington DC.

Tensions have exploded on parental Facebook groups, proponents and opponents of critical race theory – known as CRT – have both made complaints to the sheriff’s department. Security cameras have gone up outside homes.

At the centre of it all is an issue, barely heard of this time last year, which now looks set to be a major political football in the US midterm elections in 2022.

The previously obscure doctrine of CRT began in the 1970s with academics responding to what they viewed as a lack of progress following the civil rights legislation of the 1960s.

It is based on the idea that racism is systemic in US institutions, and that they function to maintain the dominance of white people in society.

Opponents say children should not be taught that America is fundamentally racist, and view it as an effort to rewrite US history, in the process persuading white people that they are inherently racist and should feel guilty because of their advantages.

Parents protesting against CRT sing the Star Spangled Banner at a Loudoun County School Board meeting

Credit: Reuters

Scott Mineo, a parent in Loudoun County who launched Parents Against Critical Theory, said: "It’s anti-white. It takes a negative position against the United States."

So far, nine US states have banned or limited the use of CRT concepts in schools, and two dozen more are considering it.

Loudoun, which has the highest average household income – $142,000 – of all America’s 3,006 counties, has become a particular flash point.

The county, which has a population of 413,000, was one of the last in the US to desegregate schools in 1967, and has had a history of racial incidents since.

Amid an influx of immigrants the white population has been falling. Of the 70,000 school pupils 43 per cent are white, 25 per cent Asian, 18 per cent Hispanic and seven per cent black.

In March, messages from a private Facebook group – “Anti-Racist Parents of Loudoun County” – were leaked.

They included a call from one member to "infiltrate" networks of parents opposed to CRT by creating fake online profiles, and to deploy hackers to "shut down their websites," and "expose these people."

The Facebook group was dubbed the "Chardonnay Antifa".

Jamie Neidig-Wheaton, a white parent and one of the group’s administrators, later said it was "benign."

She said: "One of the things they [CRT opponents] want to do is mock us and call us names. I’ve got thick skin and I’m fine with that.

"[But ] we have a school system with serious racism going on."

A rally in Loudoun County, Virginia

Credit: AFP

Meanwhile, a group of parents called Fight For Schools, opposed to CRT, has launched a campaign to recall six members of the Loudoun County School Board.

In a TV advert they said the board was "infecting our schools with critical race theory, training teachers that Christians are oppressors, and teaching children about their ‘white privilege’."

The Loudoun school system has argued it is training the mostly white teachers to be "culturally responsive" as the student population becomes increasingly diverse.

Public school board meetings have become ever more tense.

Ian Prior, a parent opposed to CRT, told a recent meeting: "It is this school board, the administration, and a Facebook mob that has put Loudoun County as ground zero in a national fight against critical race theory.

"Every one of these parents would step in front of a train for their kids. They will step in front of you too. This is the fight of our lives."

Shawntel Cooper, an anti-CRT black mother, said: "Think twice before you indoctrinate such racist theories. You cannot tell me what is or is not racist. Look at me."

At a board meeting in late June hundreds of parents protesting against CRT turned up with placards saying "Education not indoctrination" and "You don’t end racism by teaching it."

The board walked out amid chants of “Shame on you" and police arrested two parents who refused to leave.

A man is arrested at a Loudoun County school board meeting in late June

Credit: Reuters

Afterwards Rachel Pasani, a parent who was not arrested, said: "We are an army of moms and parents that will not stop until we’re heard. This is insanity in America."

There have been protests at other school board meetings across the country, and they are expected to increase.

In Nevada, a group called the Nevada Family Alliance called for teachers to be fitted with body cameras to monitor use of CRT ideas in classrooms.

Karen England, its executive director, said: "The response has been overwhelming. Parents from across the nation are contacting us wanting help to make this idea a reality in their district."

Florida’s Board of Education recently banned CRT from classrooms.

Ron DeSantis, the state’s Republican governor, said: "Some of this stuff is, I think, really toxic. I think it’ll cause people to think of themselves more as a member of a particular race, based on skin colour, rather than based on the content of their character."

According to a recent Economist/YouGov poll 58 per cent of Americans are opposed to CRT, with 38 per cent in favour.

Among independent voters 76 per cent had an unfavourable view, and 20 per cent a favourable one.

Ford O’Connell, a political strategist, said that for the republican party "this is the issue that will get suburbanites with you."