Power is the narcotic of modern politics, and nowhere more than in the offices of contemporary prime ministers. It is extraordinarily difficult for them to relinquish power when the time comes.
This is the dilemma facing Tony Blair and his supporters as they struggle to manage a smooth transition from prime ministerial office. Once the issue of departing is explicitly raised as a scenario, as Mr Blair foolishly did last year (and later regretted), the actual deed is more likely to end up as a train crash rather than an orderly process. The warning was given by David Miliband, a Blairite minister, in the New Statesman. It is amply borne out in the sceptical response by supporters of Gordon Brown to yesterday's statement by Mr Blair that he will be gone within a year. The dynamic of enmity between them is much more likely to compress that timescale, possibly drastically into weeks not months.
Paradoxically, there is an inverse relationship between the vehemence with which the spoils of office are contested and the policy disagreements among those competing for it. Few ideological disagreements are visible between the Blair and Brown camps. Both sides insist they are politically convergent, for the good of the party. Nevertheless, Mr Blair is determined to complete his existing political agenda. He wants to lay the groundwork for another period of the New Labour policy on which he was originally elected party leader in 1994 and won the 1997 election, the first of three in which he has been victorious. He suspects the Brown camp harbours old-fashioned left-wingers who would seek to reverse that trend if their candidate succeeds. That may be why he holds on to power, awaiting the emergence of a candidate who could effectively challenge any such policy reversion.
Mr Brown may well be Mr Blair's most likely successor, but is he electable? It is 13 years since the two men made their political bargain and they now look more and more similar to one another - products of a passing era, notwithstanding their mutual political and economic success over nearly 10 years in power. Mr Blair's judgment in not encouraging a strong alternative to Mr Brown may be questioned just as much as his prevarications about relinquishing office.
This is not the time to make a definitive assessment of Mr Blair's political career, its achievements and its flaws. He has been a towering figure, not least for his dedication to transforming relations between Britain and Ireland. That is one good reason why his final phase in power is being watched with such attention here.