In the state department of past administrations, how to respond to an incendiary event such as the murder of the British student Henry Nowak would have required deliberations, memos and meetings. Given how it has roiled the UK and inflamed tensions over migration and race, the cautious diplomats at Foggy Bottom probably would have said nothing at all.

Now they tweet from the hip. “Ideological conditioning and two-tiered policing are glaring symptoms of civilizational decline,” the department’s official account posted on Thursday. “They must be rejected across the West.”

This is, after all, the state department that hosted the far-right provocateur Tommy Robinson for a tour earlier this year, has crowdsourced targets for deportation on X, and portrayed the UK – as well as much of Europe – as an ideological prison that celebrates censorship.

And it is one that has returned time and again to a thesis shared by much of Europe’s right: that mass migration has threatened the cohesion of western society and now must be reversed.

The US vice-president, JD Vance, took up that refrain late on Friday with an incendiary tweet explicitly linking Nowak’s death to civilisational decline.

“Henry Nowak died the same way a civilization dies,” Vance wrote on X. “He should still be alive today, and he would be if the last few generations of European elites had stood their ground against the politics of self-hatred and the mass invasion of migrants, many of whom despise the West and the people who love it.”

He added: “It is because we love the West that we want to preserve it. We love our civilization. We love our country. We love our children.”

Some US diplomats believe the UK had this coming. Senior Labour figures including the deputy prime minister, David Lammy, voiced their support for George Floyd, a Black man killed by a white police officer in Minnesota in 2020. Now, they argue, US officials are simply doing the same and speaking their conscience, this time to defend a white man against what they say is the scourge of immigration and double standards.

The charge into UK politics has been led by elected officials including Vance, culture warriors at the state department, and one of the world’s richest men, Elon Musk, who has posted enthusiastically in support of Robinson and the recent Unite the Kingdom anti-immigration rallies. “Send the video to everyone you know showing how heinously Nowak was treated by the police in his dying moments,” Musk wrote in one of several posts on X, the social network he owns.

On Friday, Keir Starmer responded: “Musk, again, has been interfering in our politics in the last few days, trying to whip up division – that is not who we are in Britain.”

The US animus toward the modern face of the UK comes from the top: Trump has leaned into a personal feud with the mayor of London, Sadiq Khan, whom he has falsely accused of trying to impose sharia law and under whose tenure he said the UK capital had become ridden with “the stabbings and the dirt and the filth”.

Online censorship and criminal cases sparked by social media commentary have been another focus for US officials. Vance confronted Starmer in the Oval Office over the issue last year and in an infamous speech at the Munich Security Conference said: “In Britain, and across Europe, free speech, I fear, is in retreat.”

There are standouts among the state department’s diplomats promoted into prominent positions in public diplomacy and democracy promotion who target the issues that have particularly angered conservative commentators.

Among them is Samuel Samson, a deputy assistant secretary of state for democracy, human rights and labor, who has encouraged money be set aside for a legal defence fund for the far-right French politician Marine Le Pen and has defended Germany’s Alternative für Deutschland party from being labelled as “extremist”.

Samson wrote: “Across Europe, governments have weaponized political institutions against their own citizens and against our shared heritage … Far from strengthening democratic principles, Europe has devolved into a hotbed of digital censorship, mass migration, restrictions on religious freedom and numerous other assaults on democratic self-governance.”