According to a poll published in the United States earlier this month, one in three adults believes that an attempt is being made “to replace native-born Americans with immigrants in order to achieve electoral gains”. A similar proportion sees the cultural and economic influence of US-born Americans diminishing as a consequence. The vast majority of those holding these views are likely to be white. From being a fringe notion on the extreme right, “replacement theory” appears to be entering the bloodstream of mainstream political discourse in the US.

This should be seen as an insidious, disturbing backdrop to the mass shooting that took place in Buffalo at the weekend. Payton Gendron, the teenage suspect, is charged with shooting 13 people – 11 of them black – in a supermarket in a black neighbourhood of the city. Ten died. The action appears to have been carried out alone, and the suspect reportedly posted an online “manifesto” in which replacement theory is melded with anti-black racism and antisemitic content and tropes. Most of its material seems to have been culled via solitary immersion in far-right websites. Black people, read one passage, were equivalent to immigrants in that they “invade our lands … live on government support and attack and replace our people”.

Buffalo joins Charleston, El Paso and Pittsburgh as a site of bloody tragedy, after murderous attacks by lone white attackers. Last year the FBI identified the lethal rise of far-right terrorism aimed at minority ethnic groups as the biggest domestic security threat to America. Inevitably, there will now be renewed focus on President Biden’s stalling gun control programme – the latest to come up against the seemingly insuperable intransigence of Congress and the influence of the National Rifle Association. This was the deadliest mass shooting in America in 2022, but also the 198th to claim the lives of four or more people since the turn of the year. Despite Mr Biden’s commitment to reform, improved background checks and a ban on the kind of assault weapon used in Buffalo seem as far away as ever. Social media platforms will also come under renewed and deserved scrutiny.

But there is a wider political context that needs to be recognised. The post-Trump radicalisation of parts of the Republican right has led to the cultivation of demographic and racial anxiety, succouring extremist views. Explicit references to race or ethnicity are usually absent from such interventions, allowing plausible deniability. The Fox News political commentator, Tucker Carlson, who hosts one of the most popular cable news shows in the US, regularly ploughs this furrow: in one show last year, Mr Carlson argued that Democrats are seeking “the replacement of legacy Americans with more obedient people”, who are “newly arrived from the third world”.

Channelling and perpetuating the Trumpian “build a wall” mindset, senior Republican politicians have also used the language of replacement and “invasion” in relation to the southern border. Proposals for immigration amnesties have been conspiratorially framed as a means to secure a permanent liberal majority in Washington. Meanwhile the caricature of “critical race theory” as a pro-black threat to white identity has incubated the fear of a kind of “replacement” from within. In the wake of the Buffalo shootings, Mr Biden said that hate “remains a stain on the soul of America”. The radical Republican right and their cheerleaders are coming perilously close to being its enablers.