The video that emerged this week of British soldiers in Afghanistan using a picture of Labour leader Jeremy Corbyn for target practice cannot be divorced from our toxic political moment. The instance goes far beyond Brexit, and speaks to the anxieties of an inflamed nationalism in which both Corbyn and the military play important symbolic and political roles. It also encompasses a fact well-documented in political history: that language has consequences.

Accusations of treason are now virtually commonplace in our political discourse, from the Daily Mail’s “Crush the Saboteurs” and “Enemies of the People” to Brexiteers crying “betrayal” at any attempt to contemplate a future relationship with Europe that fails to conform precisely to their own demands.

But no politician attracts such incendiary bile to a higher degree than the Leader of the Opposition. The Conservative Party, broad swathes of the media and fringes of the Labour right consistently portray Corbyn as a threat to national security. So it is unsurprising that he gets treated as such. Examples include the Brexit supporter who was recently jailed for assaulting him, the terrorist responsible for the attack on the Finsbury Park mosque who expressed the wish to murder him, and now, it appears, serving members of the British armed forces.

The idea that Corbyn is an enemy of the nation did not materialise from thin air. Leading members of the security establishment have contributed to this dangerous narrative. In 2015, a bravely anonymous “senior serving general”, warned the Sunday Times of “a mutiny” if Corbyn were elected prime minister. “The general staff would not allow a prime minister to jeopardise the security of this country and I think people would use whatever means possible, fair or foul to prevent that. You can’t put a maverick in charge of a country’s security”.

The former head of MI6, Richard Dearlove, has also described Corbyn as a threat to national security.

What precisely is the nature of this threat? An examination of Corbyn’s major speeches as Labour leader on foreign and military policy reveals a commitment to international institutions such as the UN, a strong preference for negotiation over conflict, and a focus on addressing the root causes of insecurity. This is uncontroversial stuff and, in light of a string of British military disasters in recent decades, it is hardly surprising that there is an appetite for Corbyn’s approach. His popularity and anti-imperialist stance has become a major trigger for the status anxieties of the British military establishment.

In 2015 the then chief of defence staff, Nick Houghton, expressed concern that “we are experiencing ever greater constraints on our freedom to use force”, with a lack of public support having a restraining effect on politicians. Houghton worried that “if a nation’s assumed willingness to commit to the use of force is only in the face of [a threat to] national survival, then we encourage rather than deter revisionist states and their own ambitions”.

In other words, it might only be possible to use violence for self-defence, rather than to aggressively enforce a US-led global order. More revealingly still, the mutinous general who spoke to the Sunday Times warned against “any plans to emasculate and shrink the size of the armed forces”.

The softer masculinity that Corbyn projects is certainly at odds with the self-satisfied, macho belligerence of the dominant discourse that characterises British militarism. More than his policies, or the changing political reality that he represents, it is Corbyn’s attitude that really gets under the skin of the security elite.

For all the talk of his “foreign associations”, his oldest associates on the left frankly acknowledge that, as a leading figure in the British peace movement, Corbyn has never advocated terrorist violence against civilians. His real crime is to acknowledge that Western power has often had a severely harmful role in the world, and to sympathise more with liberation struggles in the global south than with violence as a tactic.

In bringing this kind of politics into the mainstream, Corbyn has committed blasphemy against the doctrine of the British elite: that Western power is an unambiguous force for good in the world, and Western state violence a force of inherent virtue. It is this that marks him as a traitor, and – in the context of widespread anguish about Britain’s status in the world – explains the sheer viciousness and spite of the backlash against him. If Corbyn’s opponents continue refusing to engage with him as a legitimate politician with legitimate views, the consequences of their hysterics could become uglier still.

David Wearing is a teaching fellow in International Relations at Royal Holloway, University of London, and author of “AngloArabia: Why Gulf Wealth Matters to Britain”.