Nigel Farage might not match everyone’s idea of a charismatic figurehead, but his special capabilities as leader of Ukip are proven by his enduring irreplaceability. Since he stood down in 2016, the party has had three leadership contests. It is about to have a fourth.

Henry Bolton was ousted over the weekend for reasons connected to his relationship with Jo Marney, a model with a string of racist text messages to her name. It isn’t clear whether activists objected more to Marney’s opinions or Bolton’s failure to silence them.

Ukip members oust Henry Bolton as leader after only five months Read more

The party is being led on an interim basis by Gerard Batten, an MEP whose published views include the assertion that Islam is a “death cult”, and that Muslims should sign a document denouncing passages of the Qur’an. A future beckons as a vicious party of the far right, or a resource for fiendish pub quiz masters. Who was the second leader after Farage in 2016? Trick question. It was Farage again – as stand-in between the fall of Diane James and the rise of Paul Nuttall.

Ukip’s steep decline is not, on the face of it, mysterious. The party’s defining objectives were withdrawal from the European Union and tighter immigration control. Those missions have been taken up eagerly by a Conservative prime minister. So candidates to succeed Bolton will struggle to explain what the point of their party should be. Onlookers will struggle to care.

Is it inevitable that an organisation with a single ambition should atrophy the moment that ambition captures the state?

Yet I find this account of Ukip’s slide from relevance unsatisfying. Its finances and membership have dwindled as its purpose has become obscure. But why is it obscure? Brexit isn’t done yet. Is it inevitable that an organisation with a single vast ambition should atrophy the moment that ambition captures the state? Surely that is the time for such an organisation to thrive. Seen through the eyes of future historians, it is weird that the locomotive party of a revolution should shunt itself into a ridiculous siding.

Ukip never spoke for all 17.4 million people who voted to leave the EU. They had a wide range of motives. So who does represent Brexit Britain? Theresa May tried to set herself up as the spirit incarnate of the leave vote. She called a general election to confirm that exalted status and was humiliated. So now she represents haggard determination to reach next March with any kind of document attesting to the expiry of Britain’s EU membership.

A large faction of Tory MPs take a Faragist view of that method. They see compromise with the EU as treason. They have the numbers to oust May, yet they don’t. Why not? If the nation’s destiny is at stake and the prime minister is failing, surely Jacob Rees-Mogg and friends feel a moral duty to replace her. Since the prize here is said to be independence – escape from vassalage – the patience of the radical Brexiteers looks downright unprincipled. If liberty itself is as imperilled, what are they waiting for? Are they prepared to sit by as the dream is betrayed?

Play Video 0:44 Nigel Farage backs second referendum on Brexit – video

The answer is yes. The reason is also the reason for Ukip’s sudden shrinkage. Brexit isn’t a viable mass movement. It has plenty of voters and they want the referendum result honoured, as is appropriate for a democracy. Once that condition is met, the technicalities stoke few great passions. The problem for Ukip and the Tory right is an absence of actual oppressions to match the rhetoric of a liberation struggle. There were no European commission checkpoints on the roads; no gunpoint-straightening of bananas. There are no monuments to luminaries of the European project, no Jean Monnet statues to tear down; no Walter Hallstein streets to rename.

The sovereignty supposedly captured by Brussels was mostly invisible. Immigration was the exception. People who thought it had run out of control understandably blamed the EU for open borders. I suspect that resentment, or something very like it, will endure under any post-Brexit migration regime. As for the rest of it – customs unions, regulatory alignment and the like – the connection to identity and freedom is just too tenuous to sustain perpetual outrage.

If the rest of Europe had colonised Britain on the scale that Brexiteers claim, the 17.4 million leave voters would have been many more. And they would not have disengaged from the process so quickly. If Ukip had been the vanguard of a real liberation struggle, it would have millions of members. It would have a youth wing akin to Momentum, Jeremy Corbyn’s phalanx of exuberant loyalists. It would have been a magnet for bright minds; a hub of competing plans for reconstructed nationhood. Prominent leavers would be honoured as founding fathers and mothers of the restored democracy. Those Walter Hallstein streets would become Nigel Farage avenues.

Farage to claim to be voice of 17.4m Brexit voters when meeting Barnier Read more

Instead, Farage bailed and Ukip collapsed. The Tory leavers would rather complain as May does her job badly than expose themselves to the rigours of trying to do it better. Too ashamed to lead their own project, the Brexit pioneers nuzzle comfort blankets of anticipated betrayal.

This is the significance of Ukip’s slide into insignificance. A party founded on a big idea should be able to survive a change of leadership. It should grow when its idea captures the mainstream. And if that party shrivels into a ball of congealed venom, what does that say about the wisdom of its idea? It is certainly not a reflection of the majority of leave voters, who backed a cause in good faith. But it is grim to consider how the architects and advocates of that cause all turned out to be cowards and charlatans. The 52% are being betrayed, all right, but not by remainers.

• Rafael Behr is a Guardian columnist