Curiously, the reasons why some political leaders fall from office is linked to what was once their strengths rather than their weaknesses. Callaghan’s closeness to the unions was seen as one reason why he (rather than the confrontational Heath or strident Castle) would be better able to reach a workable accommodation with them, to the country’s benefit. Having undermined the “In Place of Strife” proposals it was poetic justice that it was the unions’ behaviour which destroyed his (and Labour’s) USP, forever associating the Callaghan premiership with the Winter of Discontent. Similarly, Thatcher – a politician priding herself on speaking up for ordinary taxpayers – was brought down her hubristic refusal to understand the outrage and sense of unfairness which the poll tax (an attempt to protect her beloved ratepayers) engendered.

And so to two apparently very different politicians: Blair and Corbyn. Blair’s USP was that he seemed like a trustworthy “one of us” ordinary guy, able to understand the desire for a nice house, better car, foreign holidays, unthreatening to those with assets and comfortable with the modern globalising world. Out with beards, scruffy dressing, Conference motions and old-fashioned socialism. In with branding, pledge cards, multi-culturalism and investment in public services. In the words of Rupert Everett, we could now enjoy “all-day drinking in our burkas”. Blair may not have been Labour born and bred (no Welsh mining valleys for him to reference in his rhetorical flourishes) and was perhaps more admired than loved but he was a winner.

And yet, even then, there were signs that he was rather more evasive, more slippery, less trustworthy than the image so carefully created and nurtured. When questions were raised about whether Labour policies had been changed to suit one of the party’s funders, he told us that people thought he was a pretty straight sort of guy. And then he confirmed to us that he was indeed such a guy.

He was satisfied he was honest so no reason for any of us to question the truth of what he told us. And, indeed, no-one did and anyone who tried was simply not listened to. But in that indomitable self-belief lay the hubris which eventually brought him down.

Even more worryingly, the cult of Blair – the belief that he was a winner, that there was no alternative – and that any questioning of his policies and motives was unacceptable – meant that when, finally, Blair’s beliefs finally met reality (in the Iraq war, the revelations of how the intelligence dossier had come about, the unquestioning support of the US, the apparently casual approach to the war’s legality) the betrayal and loss of trust was (and is still being) felt all the more keenly.

Corbyn’s view of Labour and personal style are diametrically opposed to Blair’s vision. His USP is socialism, old-fashioned campaigning and a principled – and very British – concern for the underdog and oppressed. It is this last which, his supporters say, explains his unfortunate tendency to be so often found in the company of or supporting those with some very unpleasant Fascistic, even Nazi-like, views, situations from which he requires the sort of careful extraction usually reserved for unexploded WW2 bombs found decades later.

In truth, Corbyn’s sympathy for the oppressed is a very qualified one. His sympathies are engaged most actively when people are oppressed by those he dislikes most. And those he dislikes most are Western imperialists and colonialists. A cynic might say that it is really the oppressor which matters to him not the victim. (The former can do nothing right; the latter nothing wrong.)

Like most politicians, he believes in dialogue with even the most unpleasant of opponents (Putin, Assad) and with anyone in order to achieve peace (hence his meetings with Hamas, a designated terrorist organisation) but curiously this privilege is not extended to those he disagrees with (“criminal” Israeli politicians, in his words, for instance). There was little sympathy for the Yazidis or Syrian or Iraqi Christians or those children poisoned by Assad or those oppressed by the Taliban. Nor in earlier years for Northern Irish Protestants killed by the IRA or Jews killed by Palestinian terrorists nor for Bosnian or Kosovan Muslims oppressed by Serbs and (eventually) rescued by Western imperialists. Still, the country has had enough of foreign interventions and Corbyn’s refusal to agree that the UK must always intervene and follow the US’s lead is popular and may also on occasion be right, however mixed or morally dubious his motives may be.

Like Blair in his prime, Corbyn’s followers will brook no dissent, no criticism, no scepticism, no forensic scrutiny. Corbyn is a good man and therefore there must always be an explanation which exculpates him, even if it makes him look like a simpleton who cannot see or read or understand what is in front of him.

The alternatives – that he may not be quite as good as he – or his supporters – think, that he can be as evasive and untruthful as most politicians or that even good men do bad things are not to be borne. The latest row about Labour anti-semitism is fundamentally seen as a PR issue, to be cured by statements rather than actions, let alone a smidgen of self-criticism or changed behaviour.

Does this matter? Probably not, electorally at least. As Mr Weinstein might ruefully observe, moral compasses are not needed by the powerful or those on a winning streak. And they can be seen as an unhelpful irrelevance to those keen for a change of government.

Corbyn dominates his party; he has been more electorally successful than many imagined; he may well end up PM. Who needs criticism, especially from those who are not true believers?

But the risk is that one day – like the Blair his party no longer cares for – his self-belief, his Nelsonian blind eye to any faults in those he campaigns for or alongside, his flexible principles, his faithful supporters’ aggressive silencing or cowing of critics, his Chamberlain-like belief in the value of dialogue even with those acting in bad faith may come face to face with reality and prove his and the Labour party’s undoing. And, possibly, the country’s.

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