As emerging reports would have it, Kevin William Harpham, 36, who is accused of setting a bomb to go off at the Martin Luther King Jr Day parade in Spokane, Washington, was yet another "lone wolf" terrorist, acting at his own behest and on his own behalf. Even groups on the racist, radical far right that so clearly inspired him are rushing to disown and denounce the indicted man. Regardless of whether he was a "member" of an organised group, there can yet be no doubt that Harpham saw himself as part of a movement – one that has an especially broad reach in the age of Obama, and roots as deep as American culture itself.Nineteen of those killed were aged under five in the 1995 Oklahoma City bombing, which before 9/11 was the deadliest terrorist attack in US history. (Photograph: Porter/Keystone USA/Rex Features)

The vision of a black president has given the racist far right one of its biggest boosts since the civil rights era of the 1960s. Figures toted up by the Southern Poverty Law Centre suggest a dramatic rise in the numbers of organized groups: their numbers grew by 40% from 2008 to 2009, and an additional 22% from 2009 to 2010, bringing the total to 2,145 groups. It's difficult to know precisely what these numbers mean, since these groups are constantly changing names, dissolving, reforming or springing up, and few of them maintain public membership rolls. What is nonetheless clear is that a strong far right movement has re-emerged, and what unites it is the age-old American doctrine of nativism, born out of fear of some dark outsider sneaking in to steal the white man's homeland and his hegemony.

Nativist thinkers are spread all over the map, but the strongest current comes in the form of the Sovereign Citizen movement, or what used to be called the Posse Comitatus and before the posse, the Silver Shirts. For the old Posse adherents and their contemporary progeny, the white Aryan man is the only true "sovereign" over his land and his life. White women serve beneath him; black and brown "mud people" are menials worthy only of disdain; and Jews (who do not qualify as white) are usually behind it all, running the economic and financial systems through a worldwide Jewish conspiracy. They do not admit to being subject to the laws and dicates of the US government; they eschew social security, cars and drivers' licences, and won't pay taxes.

For the true sovereign, the sheriff is the highest legitimate law enforcement official in the land, and a jury of his (white male) peers the only legitimate government body. These beliefs are underpinned by the religion of Christian Identity, which claim white sovereigns are the direct descendants of the lost tribes of Israel, who on their long trek out of the Middle East made their way up through Scotland and Ireland over to the United States.

Different facets of the nativist movement have enjoyed periodic heydeys in 20th-century America – first in the 1910s and 20s, when anti-immigrant sentiments were rife and membership in the Ku Klux Klan reached more than 2m. In the 1930s and 1940s, they penetrated the edges of the political mainstream through figures like Father Charles Coughlin, who was the Glenn Beck of his day. A Catholic priest and radio personality, Coughlin was at once enormously popular and virulently antisemitic and anti-New Deal. His ally Gerald LK Smith, leader of the Share Our Wealth campaign, was evocative of some of today's more extreme Tea Party candidates.

The Klans and related groups had another resurgence in response to the civil rights movement of the 1960s. In the 1980s, groups like the Posse, which drew together white supremacy and Christian Identity with anti-government "patriot" sentiments, found particularly fertile ground for recruitment among dispossessed Midwestern farmers. While figures like David Duke ran for political office, others, like the violent group The Order, carried out bombings, bank robberies and murders, and engaged in blazing shootouts with federal agents, all in service of their plan to build a white homeland.

After the Oklahoma City bombing, with its perpetrators' ties to the militia movement (and, most likely, to other far right groups as well), the movement tended to dig in further underground. Just as Timothy McVeigh and Terry Nichols were deemed to be acting alone, the periodic bursts of far right violence – whether they be an attempted bombing, the murder of an abortion doctor, attacks on undocumented immigrants or on Muslims, or the shooting of a congresswoman – are attributed to "lone wolves" rather than to organised plots by any particular group. Yet the distinction belies the reality of a movement that has long encouraged its adherents to act in "leaderless resistance" cells or carry out one-man guerrilla attacks (and become celebrated as "Phineas Priests", named for the Bible story of a man who executed an interracial couple).

The alleged MLK Day parade bomber, Kevin William Harpham, may or may not have consider himself a lone wolf if, as he is accused, he put together a backpack bomb laden with shrapnel dipped in rat poison to induce bleeding and placed it on the route of the parade. But there can be little doubt as to where his inspiration came from. Bill Morlin, formerly a reporter for the Spokane Spokesman-Review and now an independent investigator, traced Harpham's background in a comprehensive report for the publication Hatewatch. In the military, Harpham was stationed at Fort Lewis in Washington, home base for 320 far right wingers. He was once a member of the racist far right National Alliance, and had left various postings on extremist websites suggesting he had had enough of the "international Jewish conspiracy", which, among other things, he held responsible for 9/11.

Leonard Zeskind, a leading expert on the radical far right and author, says that today, "the main tendency of organisations is mainstreaming … The movement imperative is towards the Tea Parties, running for office, anti-immigrant mongering – not roadside bombs." None of this, of course, prevents people from being "recruited" to their ideas and choosing to act on them. One far right leader said much the same in an interview following the attempted bombing in Spokane. "There are many aspects to the white supremacist movement," Shaun Winkler, Imperial Wizard of the White Knights of the KKK in Idaho, told a local television station. "There are those of us that are on the political side, and there are those of us that are revolutionary. It sounds as if this individual was on the revolutionary end rather than the political. And there are a lot of lone wolves out there. People that are sympathetic to us, but people that we don't know."

Historically, federal law enforcement has given little credence to the power of the nativist current in American society, and has paid relatively little attention to the activities of nativist groups. That has perhaps changed since the election of Barack Obama, whose presidency has so focused and emboldened the racist far right. Yet, despite their obvious threat, there are no competitors to Peter King, holding congressional hearings on the recruitment of homegrown jihadist terrorists.