“We go forward as a movement and a party, stronger, bigger and more determined than we have been for a very long time,” declared a jubilant Jeremy Corbyn in September 2015, freshly anointed as leader of the Labour party. “We are going to reach out to everyone in this country, so no one is left on the side, so everyone has a decent place in society.”

Fast-forward nearly five years – via one referendum, two election defeats, and the most turbulent period of constitutional debate for a generation – and the Corbyn era is finally drawing to a close. On Saturday, Corbyn’s reign of error will end and a new leader will be named, most likely shadow Brexit secretary Sir Keir Starmer.

The Labour leader will leave behind a party in tatters, neither strong nor particularly determined, that in December last year manifestly failed to reach out even to communities that had voted Labour for generations. His legacy will be one of shambolic disappointment, leading his party from the heights of Corbynmania to its worst defeat since 1935.

Corbyn’s history and personality were always going to make him unsuitable for the top job. More suited to championing niche and often controversial causes abroad than focusing on the nitty-gritty realities of government at home, he never seemed to realise that his main task was holding the government to account.

Even at the most disastrous moments of Theresa May’s premiership, Corbyn’s performances at PMQs were lacklustre and off-topic. Instead of honing in on glaring government errors, he preferred to ramble through pre-prepared questions that often had little to do with the crisis at hand. He was utterly unable to adapt. And his refusal to even acknowledge, let alone apologise for, his dubious associations with terror groups and dictatorial regimes over the years (from the IRA to Hamas, Iran to Venezuela) meant that there was always another scandal ready to come to light just when the Conservative government needed to distract attention from its own failures.

And failures there were aplenty. But while May staggered from Brexit crisis to Brexit crisis, on the most important issue of the last four years (until coronavirus struck), Corbyn had virtually nothing to say. His lifelong career of euroscepticism put him at odds with the majority of his MPs, meaning that Labour never quite had a comprehensible Brexit policy. May’s numerous defeats in the Commons came at the hands of her own party, not from the official opposition, while Labour’s Brexit strategy was characterised by zigzagging and infighting between the various factions, with leadership from the top always absent.

Instead, the Corbynite movement focused inward, concentrating on infiltrating and controlling the party machinery. From local constituency parties to Labour’s national executive committee, Corbyn’s Momentum acolytes took over, dominating policy debates, pushing the party ever-leftwards, and even attempting to deselect MPs deemed at odds with the Corbyn project. On Corbyn’s watch, the aim of those at the top of Labour shifted from winning elections to purging all but the most pure.

With dissenters silenced, there was a cult-like atmosphere around the leader’s office. Criticism of the Dear Leader was consistently dismissed as a “smear campaign”, and any kind of analysis of Labour’s prospects or popularity was rejected as disloyalty. When Labour members, and sympathetic journalists or commentators, attempted to sound the alarm about the direction in which the party was headed, Corbyn’s army of keyboard warriors jeered at them to “f*** off and join the Tories”. They seemed surprised when, in December, many of Labour’s former voters opted to do just that.

This myopic insistence that criticism was not worth responding to meant that Labour was never able to recover from the repeated anti-semitism scandals. It lurched from one to the next. It meant that, when seven MPs quit Labour last year in protest at Corbyn’s leadership, the party never paused to consider who else it might be alienating. And it meant that, even after voters had robustly rejected the vision of nationalistic, high-spending, big state control laid out in the Labour’s 2019 manifesto, Corbyn had the audacity to insist that he had “won the arguments”.

Today, of course, statism and high spending are back. Corbyn has used his final days as leader to argue that the government’s reaction to the coronavirus pandemic – opening the spending taps to support business and individuals devastated by the Covid-19 impact, pouring money into public services, wracking up debt and intervening in the private sector – proves that he was right all along. It is delusional.

The fact that, even now, he cannot see the difference between an emergency response to a global crisis on the scale of a war and his template for day-to-day government demonstrates that he should never have been allowed close to a position of power.