The most extraordinary aspect of the scandal over spending irregularities that has destroyed Shane Jones' leadership aspirations - and possibly his entire political career - is that he ever imagined he might get away with it.

Jones, the Building and Construction Minister in the last Government, has been the most conspicuous casualty of the furore because of the nature of some of his expenditure: adult movies watched in hotel rooms.

In numerical terms, Jones is not in fact the worst offender in the latest round of revelations: his one-time colleague in Cabinet, Education Minister Chris Carter, actually ran up 33 per cent more than Jones - on flowers, designer clothing and spa treatments.

Most gallingly, he used his ministerial card to buy flowers for Lianne Dalziel after she was sacked as Immigration Minister for lying about having leaked documents to a television channel.

The logic by which he could regard it as a ministerial duty to console a colleague who had sought to deceive the public remains obscure to everybody but him, it appears.

There is a case to be made that the unauthorised spending is nowhere near as bad as it appears and that its sleazy nature gave the matter a higher profile than it deserved on its merits.

The entire quantum of improper expenditure looks likely to be a good deal less than the $50,000 cost of disclosing it and the fact that much of the money had been reimbursed before the story broke meant no criminal conduct had occurred.

But these ministers spend public money, a commodity in short supply. It is entirely proper that there be strict procedures to ensure it is wisely spent.

And principal among them is the requirement that no personal expenditure be incurred on a ministerial card. That means precisely what it says: it does not mean that it is all right to run up private expenses with the intention of later reimbursing them.

Many of us run two or more plastic cards and make daily decisions about which to use, for reasons of our own personal accounting. It is no great burden to do so, and it is the least we might expect of someone carrying a card for which the taxpayer picks up the tab.

The mindset of someone who would disregard such rules is fertile ground for speculation. It is not enough to plead carelessness, since Ministerial Services explicitly reminds ministers about the rules when unauthorised spending is detected and earmarked for reimbursement.

It may be that there is simply a self-important sense of entitlement at work. But more disturbingly it is plausible that disregarding the procedures is a form of trying it on: knowing that the statements will be scrutinised makes it worth waiting to get caught before protesting honest intentions.

The events of the week have surely irretrievably damaged the mana of a man who was widely tipped to succeed Phil Goff as Labour leader and, in the eyes of many, potentially the country's first Maori Prime Minister.

Sad though that is, there is a sense here of history repeating itself. Winston Peters and John Tamihere were in their turn cloaked with the mantle of future premiership.

Both in their different ways showed that they were incapable of the tactical finesse required to navigate the treacherous waters of politics. Whatever aspirations to true leadership they may have had now lie in ruins.

The same probably goes for Jones. Bilingually at ease in Maori and Pakeha worlds, he is an extremely able and well-qualified politician.

But he destroyed his prospects by deciding - certainly stupidly, possibly arrogantly - that there was no need to finance private activities with private money.

At the very least, his judgement will be permanently suspect. And meanwhile Maori will be excused for wondering how long they must wait for another likely candidate for the top job to emerge from their ranks.