Politics is a brutal business, a contact sport where success demands not only strategic cunning but absolute ruthlessness. The minimum requirement for the ambitious politician with an eye on victory is the ability to smash through the other side’s arguments – but getting past opposition defences is only half of it.

Truly significant politicians – people such as Tony Blair, Margaret Thatcher and Alex Salmond, who achieved a number of their objectives and left considerable legacies – are also willing to turn, mercilessly, on allies. One does not come first without nobbling teammates whenever it is expedient to do so.

In the strange, paranoid, frenetic world of politics it is understood, across the spectrum, that there is nothing personal about this kind of thing. One must not blame the player, but the game.

And so, at a certain level there is a camaraderie among even political rivals. When an opponent is clearly defeated, they back off. When scandal or rotten luck brings another down, thoughts turn to the grace of God.

The ongoing humiliation of former First Minister Nicola Sturgeon has evoked no such feelings in either opponents or former colleagues.

After Ms Sturgeon’s estranged husband, former SNP chief executive Peter Murrell, pleaded guilty last Monday to embezzling more than £400,000 from the party’s accounts, there was little sympathy for a women caught up in a mess of a man’s making.

Even though Ms Sturgeon was down, opponents and former allies kept kicking.

The woman who once harboured fantasies of leading Scotland to independence, thus securing her place in the history books as a global stateswoman, is now a pariah in the political village. Not only does she find herself persona non grata with the current leadership of her party, opponents are positively gleeful about her circumstances.

One former colleague, who served under Nicola Sturgeon during her time as First Minister, offers a clear-eyed view of why she now finds herself almost universally loathed among the political class.

‘People don’t like bullies,’ said this retired politician. ‘And Nicola’s a bully.’

Former colleagues are furious about the way in which she handled concerns over SNP finances, shutting down questions about party accounts at the same time as Mr Murrell was abusing his position to steal hundreds of thousands of pounds.

Opponents, meanwhile, are positively gleeful about the downfall of a woman who has so often delighted in the humiliation of others.

A recurring theme in conversations with Ms Sturgeon’s former colleagues and political opponents is her personal coldness.

A former senior SNP staffer said an on-camera moment on the night of the 2019 General Election offers a sharp insight into her character.During a live interview, news broke that the then Liberal Democrat leader Jo Swinson had lost her East Dunbartonshire seat to the Nationalists.

Naturally, Ms Sturgeon was pleased with the victory but the manner of her celebration left even colleagues uneasy.

Clenched fists pumping the air, the then SNP leader revelled in her contemporary’s political demise as if she had been standing on a football terrace.

Ms Sturgeon later issued a statement saying she commiserated with Ms Swinson on a personal level.

‘Of course we wanted to do in Swinson,’ said that former staffer. ‘That’s the objective but, you know, when you’re a First Minister, you should always be thinking about the fact that not everyone voted for you. She looked graceless and cruel when she should have been going for magnanimity.’

Another former colleague described a stark contrast between the public Nicola Sturgeon, the selfie queen, crowded by adoring supporters whenever she set foot on any campaign trail, and the private politician who could treat those around her with contempt.

‘Nicola promised people into cabinet and then treated them like idiots. You’d get the odd person like Jeane Freeman when she was health secretary who had enough about them that Nicola would treat them with a bit of respect, but the way she’d talk to other members of the cabinet was wild.

‘She wasn’t a ranter like Alex Salmond. He’d properly lose his s*** with people. He’d be going full hairdryer at someone and you’d be just trying not to catch anyone’s eye. With Nicola it was really horrible grinding passive aggression. Sometimes it felt like something out of the school playground.

‘If she thought some cabinet secretary was out of line, she could make their lives miserable – snappy, one-word answers, rolling the eyes, all that.’

This observer of Ms Sturgeon’s career went on to clarify what sort of behaviour might have been thought ‘out of line’.

‘We’re not talking about policy stuff. She hardly rated anyone on policy or delivery. Half the time, if some minister suggested something at cabinet, she’d look at them like they were an idiot. Being out of line in Nicola’s eyes was saying or doing anything that raised your profile in any way. She needed to be the centre of attention.’

Nothing unusual about that, surely? No political leader ever succeeded without a healthy ego. ‘There’s a fine line,’ said one former colleague, ‘between thinking you have the answers and thinking you are the answer and Nicola crossed it. It’s not her fault she went a bit nuts but she went a bit nuts.

‘The party was polling really well and she was getting great approval ratings and she started thinking it was all down to her. It was like all the work Alex Salmond had done to get us to where we were meant nothing.

‘She’d acknowledge him as a mentor but that was all performative. She thought she was the SNP.’

Ms Sturgeon’s estranged husband encouraged the idea of his wife as the party’s saviour. As chief executive he signed off payments on enough ‘I’m with Nicola’ branded tat to keep the descendants of Del Boy Trotter ducking and diving for generations.

It was Mr Murrell who arranged the rock star-style tour of the country where Ms Sturgeon took to the stage to the roars of adoring crowds.

‘Sturgeonmania was definitely a thing for a while,’ said one SNP insider. ‘If you think back to 2014 when she was taking over from Alex, not only was she already really popular with SNP members, but Unionist voters who by that point hated the bones of Alex, thought she was a more attractive option.

‘Back then, the Nicola Sturgeon story was reasonable young woman takes over from unreasonable old man. You had Unionist voters who thought after they won that she was going to be more, I don’t know, sympathetic, maybe?

‘The focus groups definitely told us that No voters liked her a damned sight more than they liked Alex but we weren’t hearing that she was going to suddenly convert all the people we needed overnight.

‘But Peter organised this victory tour and she ended up standing up in Glasgow in front of thousands of screaming people and I think she started to believe what she was experiencing was how the public felt about her, instead of how the party did, or how the party was being directed by Peter to feel about her, if that’s not too cruel.’

As the myth of Sturgeon as one of the political giants grew, so she became more isolated, more immune to persuasion that she might be wrong.

One former party strategist said that Sturgeon was at her most intransigent when it came to the issue of gender reform.

‘Nicola bought in to the trans women are women idea very quickly,’ said one former MSP. ‘She was absolutely clear that she was going to reform the Gender Recognition Act and anyone who thought this was a bad idea was left in no doubt that dissent was potentially career-ending.

‘The whole controversy over self-ID really brought to the surface the less appealing aspects of her character. The thing with Nicola is that she doesn’t think she’s right about a subject because the facts tell her so, she thinks she’s right because she believes in her own moral superiority.

‘If you listened to her speeches, she sounded like a preacher. It wasn’t just that other people were wrong, they were bad and she brought that attitude to anyone in the party who thought she might have got it wrong.’

Under Ms Sturgeon’s leadership, feminist politicians such as the former MP Joanna Cherry were ostracised. When, as happened in the cases of Ms Cherry and several other female politicians, trans activists issued threats and abuse, Ms Sturgeon did nothing to help. She neither called for calm nor reached out to those who were affected.

‘If you didn’t agree with Nicola on trans issues, you deserved everything you got,’ said one former colleague.

Ms Sturgeon was once, by some margin and for some time, the most popular politician in Scotland.

Friends muttered about post-office superstardom. There was talk about the possibility of her becoming a United Nations ambassador. Nonsense, I’m afraid, because there was precisely no chance that any UK Government would ever nominate a senior SNP politician for such a role.

But the fact that the idea was entertained gave us some idea of Ms Sturgeon’s relative status. Now that status has gone. Ms Sturgeon is a failed politician who turned on critics with a relish bordering on cruelty and treated her colleagues like idiots.

There will be no magnificent third act to the former First Minister’s career, no elegant slide into the role of elder stateswoman, no career as a great public speaker.

Instead, Ms Sturgeon has, while trying and failing to explain away her part in shutting down questions about money stolen from SNP members, completed her downfall.

There is no coming back from this. Nicola Sturgeon has lost all political credibility and she has lost the trust of former colleagues and supporters.

This is her legacy.