In the war of words over fishing rights in the Channel, much attention has been paid to a single line in a leaked letter from Jean Castex, the French prime minister, to Ursula von der Leyen, president of the European commission. The nuances of the offending sentence vary in translation, but the gist is that European public opinion should be left in no doubt that there is more pain associated with leaving the European Union than staying in it. To the Eurosceptic ear, that was confirmation of a spiteful motive on the continent. France, it was alleged, wants to “punish” Britain for choosing freedom. Viewed from the other side, Castex was merely restating the obvious logic of Brexit: it is a repudiation of European solidarity and a bet on the advantages that a sole trader might gain in rivalry with a syndicate. The syndicate members have an interest in that gamble not paying off. British Eurosceptics are weirdly prickly about that banal strategic fact. It is simply the corollary of their own florid rhetoric down the years, denouncing Brussels as a parasite that saps national vitality and extolling Brexit as proof of EU obsolescence – the first step in a great unravelling. Self-evidently, the European project is bolstered if Boris Johnson is humbled, and vice versa. In the fisheries dispute, France deserves an ample portion of blame for cynical escalation. President Macron is sabre-rattling with an eye on his domestic audience ahead of elections next year. But his attitude is coloured by seething contempt for a British prime minister whom he sees as a stranger to probity. That feeling was much aggravated by the recent poaching of a lucrative defence contract to build Australian submarines as part of the Aukus security deal with Washington. But it is Johnson’s treatment of the Northern Ireland protocol in the Brexit withdrawal agreement – signing a treaty with no intention of implementing its terms – that convinced the French president that Downing Street had gone full rogue. The crisis in Northern Ireland is vastly more dangerous than a kerfuffle over cod. But they are symptoms of the same syndrome: a Brexit model that makes a sacred principle of sovereignty. All trace of EU institutional leverage must be scoured from the land and dredged from the sea. That fixation guarantees tension at every frontier where old, free-flowing habits are subject to the friction of new checks, forms and licences. The material gains from maximising sovereignty in this way are nil, while costs are mounting. But conceding that the model is flawed is unthinkable in Johnson’s Tory party. Or rather, unsayable. There are MPs who understand what has gone wrong but anticipate only ostracism if they were to speak out. That leads to two policy choices. First, exaggerate or invent fictional benefits from scrapping EU rules. Rishi Sunak dabbled in this with his budget speech last week, disingenuously presenting cuts to alcohol duty as a Brexit dividend. (Booze classifications will indeed diverge from European directives, but the accompanying price drops would still have been permitted.) Second, turn international rancour to domestic political advantage: cite cross-Channel disputes as proof of Brussels’ malevolence, then rebadge the economic pain intrinsic to Brexit as a vindictive backlash from the continent. Already this tactic is being rehearsed in Northern Ireland. What the EU calls implementation of a signed agreement, Eurosceptic hardliners denounce as a blockade. It is a feasible political strategy, albeit a nasty one. But it lacks one crucial element: the heroic destination. Throughout history, revolutionary movements have made excuses for their failures by blaming foreign sabotage. But they have also sustained momentum with visions of a utopian future. That was the Brexit method, too, for as long as EU membership could be made the scapegoat for a whole range of social and economic ills. Now the ills remain but the proposed remedy has already been taken. In that sense (and only that one) Brexit is a victim of its own success. Britain cannot get any further out of the EU. Frost is scraping the sovereignty barrel. The Tory awkward squad that hounded David Cameron into a referendum, and then harried Theresa May out of office for seeking compromises with economic reality, got all they could have wanted from Johnson. They know their battle is won and are saddling different hobby horses, riding out to new fronts in the culture war, grumbling about the cost of cutting carbon emissions in the tone they once used for “Brussels’ red tape”. Johnson has tried to sustain the rhetoric of Brexit as sunlit upland. His party conference speech last month promised a high-wage, high-skill economy that would spring up in the absence of migrant labour. But that was an essay-crisis utopia, cobbled together from scraps of news about labour shortages and broken supply chains. Besides, by far the most memorable thing Johnson ever promised about Brexit is that he would get it done. That legacy is diluted every time the issue foists itself into the news, as will keep happening. The hunt for purer sovereignty will generate tension with neighbouring countries, which will then be cited as proof that only the purest sovereignty will suffice. This is not the typical revolution where the ends can justify the means. The ends have already been reached. EU membership has expired. We are stuck instead in the purgatory of endless means: a sisyphean nightmare of rolling negotiations that reach a certain point of agreement before breaking down and restarting. Johnson’s Brexit condemns Britain to re-enact forever the tedious, embittered process of leaving with no hope of satisfaction, because we have already left. Rafael Behr is a Guardian columnist