Masked men who drive terrorised families out of their homes cannot be called protesters, since the word implies legitimate grievance. The outbreak of racist violence in Northern Ireland this week is connected to the politics of migration, but not in the way that the mob and those who incited it claim.

The ostensible trigger was a brutal assault, partially captured on video. A man of Sudanese origin has been charged with attempted murder. The footage was widely shared online. The attack was depicted as part of a wider threat to white Britons by foreign “invaders”. Far-right agitators summoned vengeful crowds. Stephen Yaxley-Lennon, the activist who campaigns as Tommy Robinson, was instrumental in this process. So was Elon Musk, the billionaire owner of X, whose platform helped mobilise racist fury.

Mr Musk habitually intervenes in UK politics. Last year, he addressed a rally organised by Mr Yaxley‑Lennon via video link. He called for the removal of the current government and........

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