In the early hours of Friday's massacre in Oslo, the initial working assumption of news-watchers, journalists and bystanders was that this was likely the work of Islamic jihadists. That it was not took some time to trickle out: news reports published as late as Saturday included compiled condemnations of the attacks by Muslim leaders, and comparisons to other al-Qaida-type terrorist acts. That the attack was, in fact, masterminded by Anders Behring Breivik, a 32-year-old Norwegian with a murderous vendetta against multiculturalism, progressive government and a penchant for US Islamophobic blogs, reflects the strange distorting mirror of the current immigration and national identity debate going on in Europe and America.

What began, over a decade ago, as a far right assault on immigration policies of European countries from within (think Vlaams Belang in Belgium, the Front National in France, the FPO in Austria, to the rantings of Geert Wilders in Holland) has been exported to the United States where our ultra-conservative bloggers have handily repackaged that material. Though we in the US have not had the same economic conversations about immigration and Muslim communities – European concerns began with so-called "guest workers" who became permanent residents – the Oslo murders tragically expose a well-integrated transatlantic network of fear and hatemongering.

Among other references in his 1,500-page "manifesto", Breivik quotes favourably Robert Spencer, who runs the Jihad Watch website, Pamela Geller, who, via her Atlas Shrugged blog, was a key player in the controversy over the Cordoba House's "Ground Zero Mosque" in 2010, and Bruce Bawer, whose book While Europe Slept: How Radical Islam is Destroying the West From Within warns of the intent of Muslim immigrants to Arabise Europe.

In recent hours, each of these authors has condemned the links journalists have made to their work and the killings in Norway, calling the connections ludicrous – likening them, in statements by Geller and Spencer, to Charles Manson using the Beatles' song "Helter Skelter" as a plan for his murders.

They continue to claim their cause is just, that Islam remains a menace, though they fear a blow to their cause – yet, all without acknowledging this terror was wrought by a man who took their words to their most extreme conclusion. Spencer writes:

"The Breivik murders are being used to discredit all resistance to the global jihad and Islamic supremacism. But we're stealing it back … Islamic texts and teachings, and frequently imams, directly exhort their followers to commit acts of violence. I do not. Nor does anyone else in the counterjihad. There is nothing Breivik could conceivably have read here as a justification for killing anyone. There is plenty in the Qur'an and Sunnah that jihadists can and do use as justification for murder."

Writing in the Wall Street Journal, Bawer mourned that:

During the hours when I thought that Oslo had been attacked by jihadists, I wept for the city that has been my home for many years.

But once he realised this was not the scenario, Bawer's sympathy with the victims apparently dissolved into dismay at the probably setback to those who oppose Muslim immigration.

"When it emerged that these acts of terror were the work of a native Norwegian who thought he was striking a blow against jihadism and its enablers, it was immediately clear to me that his violence will deal a heavy blow to an urgent cause."

Of course, neither Spencer, nor Geller, nor Bawer put the gun in Breivik's hands. And while the New York Times highlighted the issue of these blogs' influence on Breivik, their Islamophobic discourse is far from an exclusively American problem. We've just taken it and run with it.

What we're seeing in the US is a successful, almost mainstream, re-imaging and repackaging of the panic of European Islamophobia, of the sort that's oft spouted by far right groups from Austria, to France, to the United Kingdom. In the year since the so-called Ground Zero Mosque furor, when campaigners brought in Europeans like Geert Wilders to march for their cause, a group of conservative Americans have become increasingly vocal in their opposition to public displays of Muslim life, from opposition to mosques (which has coincided with an increase in arson attacks) to warning calls that sharia law is soon to replace our justice system.

Partly, the success of our bloggers' ideology stems from America's vigorous free speech laws. On this side of the Atlantic, first amendment rights are guarded, rightfully, zealously and carefully. We can be more aggressive in our stances. But partly, their success comes from their very visibility: Geller, Spencer and, especially, Bawer are more mainstream in the US dialogue on Islam than their counterparts in Europe. Bruce Bawer's op-ed was published in the venerable Wall Street Journal. Pamela Geller is a regular on talkshows, from right to left. Their positions, like it or not, have found an audience and gained traction, if not wholesale legitimacy, in the US context. Their work has enabled Americans like Juan Williams, the former NPR correspondent who was fired for telling FoxNews he finds Muslim travellers on planes frightening, to bounce back with his new book, Muzzled.

It's not just talking heads, but politicians: as Peter Beinart pointed out in the Daily Beast this week, Herman Cain, a Republican candidate for the presidency, has said he would not appoint a Muslim to his cabinet, should he be elected. Cain may be a wildcard, but he's not alone: other Republicans – including Tim Pawlenty and Newt Gingrich – have expressed equally rightwing positions on Islam, expressing fear about the "Islamicisation" of America and setting themselves up as defenders against sharia law. Those messages legitimise Islamophobia, and provide a drumbeat for action for those inclined to hear it that way.

This is the ideological underpinning that motivates militias and terrorists. The Norway attacks, it might be said, were the work of a militia of one, a single man with the deranged idea that he had to destroy his society to save it.

Spencer, Geller and Bawer each create the impression that western civilisation is under threat. It was not always this way. The United States once resisted that European narrative – both because we are a country of immigration and because many Muslim immigrants came in at a higher socio-economic and educational level, while a large proportion of American Muslims were converts from Christianity. Muslims in the US were, for these reasons, perceived as better integrated into our multicultural society. But that perception has changed.

As these blogs flog these issues, day after day, a siege mentality in certain corners of the extreme right is now pervasive: our culture, they say again and again, is being Islamicised. If we don't defend ourselves, the implication is that "we" will be overtaken and "our" culture will disappear. Is it not justifiable, then, in such a rhetorical atmosphere, to ask: if you are promoting the idea that people are facing an alien invasion, is it not reasonable to assume that there will be those who hear that as a call to arms?

It is hard to feel much sympathy for these writers, as they complain of their maligning in the mainstream press. Sympathy, in any case, is beside the point, for in fact, they thrive on the marginalisation.