Jeremy Corbyn has won the Labour leadership triumphantly, against all odds and predictions, and with a level of support that renders the result utterly conclusive. He has not won the right to lead a country.

Some of his supporters talk as though government is not their first order of business. Mr Corbyn’s despairing opponents have argued, in contrast, that in politics government is everything, that ordinary voters are more interested in achievements than in philosophical arguments. Labour’s leadership contest has been a fight, in essence, between pragmatists and idealists.

This morning, instead of damning Mr Corbyn as archaic and unelectable – a tactic that got them nowhere – his opponents might ask why their candidates were rejected so completely. There might be satisfaction in claiming that “Labour has gone mad”, but it hardly counts as analysis. There might equally be truth in the claim that the new leader will be spurned by voters. Are those who have just suffered a crushing defeat best qualified to judge?

Saturday’s result was an obituary, patently, for New Labour. The fact is obvious, the reasons less so. What became of the grand “project” devised by Tony Blair and Gordon Brown? Was it so fragile, so transient? Was its appeal to the party itself so superficial? The questions are fundamental to the conflict between Labour’s factions. Given the choice, the mass of members and affiliates have disowned a political formula that won the party three general elections in succession.

It is more than perverse. It speaks of a profound frustration verging on disgust. Whether the accusation is fair or not, the party has registered contempt for what Labour was perceived to have become. An ideological drift into Tory territory? The fixation of out-of-touch identikit MPs with what they called the political centre? Eighteen years after Mr Blair won office, rejection is absolute.

An error of historic proportions might have been committed in the process, but those who take that view must explain why their politics alienated colleagues and comrades so thoroughly. Labour might be heading towards a political cul de sac as its traditional support shrinks away. Nevertheless, Mr Corbyn has succeeded because the New Labour idea has failed within the party itself.

For him, that is scarcely half the battle. “Authenticity”, principles and passion might impress the faithful, but they are no substitute for policies. Mr Corbyn is proof that there are second acts – or is it third? - in British political lives, but the task he faces is daunting indeed. Can he win back Scotland? Can he really appeal to the former Labour voters who have drifted towards Ukip in England? Why should anyone alienated by the Liberal Democrats turn to his full-blooded socialism?

The usual answers to such questions explain why the new leader’s defeated opponents are so dismayed. A clutch of them have already refused to serve in his shadow Cabinet. That is their right. It also makes sense: if honest politics is the order of the day, there is no point in shadow ministers pretending to support Mr Corbyn over Nato, Europe, or control of the Bank of England’s printing presses.

Much of the detail of such policies remains to be fleshed out. No one truly knows how Mr Corbyn will perform as leader of the Opposition amid a determined Tory attempt to destroy his credibility. The only important judgment lies, as ever, with the electorate.

Mr Corbyn maintains, in effect, that voters have been misunderstood, misled and misrepresented. Received wisdom says he is utterly wrong. We shall see.