President Olusegun Obasanjo has done his best to make coups a thing of the past, purging the army of politicized officers and pampering the Brigade of Guards, which sits behind the presidential villa. Mr Obasanjo's grip on Nigeria's spooks has kept him ahead of coup plotters: an alleged assassination attempt last year was foiled before the plotters could procure the missile to shoot down his helicopter.  Yet Nigerians still fear for their country's stability.

In September last year, a bandana-wearing, speedboat-driving, Kalashnikov-toting gentleman called Mujahid Dokubo-Asari threatened “all-out war” on the Nigerian state if his ethnic kin, the Ijaws, were not given more of the profits from pumping oil out of their homeland. Mr Asari, the son of a judge and proud descendant of Ijaw slave traders, commands a militia force of unknown strength but proven ability to cause mayhem.

Since late 2003, fighting between Mr Asari's men and those of a rival militia has cost hundreds of lives and caused tens of thousands of people to flee their homes. Mr Asari's men have fought battles not only in the mangrove swamps but also, brazenly, in the streets of Port Harcourt, the biggest oil town. The police have tended to run away, since they “don't have the firepower in comparison to the militia,” as a police commissioner told Human Rights Watch, a pressure group.

Mr Asari's pose as the champion of an oppressed people strikes some observers as risible. Most of his victims have been Ijaws. And if he really plans to share the oil wealth more fairly, that would be a radical innovation. The Delta's villagers are among the poorest in Nigeria, though its governors are probably the richest. Although Mr Asari allegedly first rose to prominence as an enforcer for a state governor, he now draws his strength from public anger at the government's failure to reverse decades of neglect. For the Delta's legions of jobless youths, joining a militia such as Mr Asari's can provide both a pocketful of cash and a sense of purpose.

President Obasanjo has tried to defuse matters. In October, he brokered a ceasefire between Mr Asari and his main rival, a militia boss called Ateke Tom. Both groups have surrendered some guns in exchange for generous compensation. Mr Asari now lives in a spacious two-storey villa in Port Harcourt and swans around in a leather-lined Lincoln Navigator.

Rewarding thuggery is perhaps not the best way to curb it. Mr Asari has not stopped talking about his “armed struggle” for an Ijaw nation. He boasts that he can buy better weapons with the money he received for the old ones. Most worryingly for the government, he retains the ability to disrupt the oil industry.

“This is an example of how you turn off a flow station,” Mr Asari told journalists on a visit to the twisted wreckage of a pipeline near the town of Bukuma. That pipe was abandoned years ago, but Mr Asari's message is clear.

Given the Delta's maze of creeks, it only takes a few dozen fighters to inflict serious damage. Mr Asari used to brag about stealing oil (oil that rightfully belonged to the Ijaws, he said). Now he claims to earn his living as a private security contractor. The big oil firms all deny hiring him, but sub-contractors escorted by police were seen last year begging his “permission” to operate near one of his hideouts.

The oil companies are in a sticky position. Shell and ChevronTexaco have publicly committed to ending unorthodox payments. But one Shell contractor said he still faced pressure to meet production deadlines, which meant somehow dealing with threats to disrupt the flow of oil. “We may not want to, but we do what is necessary,” he said.

The army is supposed to protect oil firms, but its soldiers have an inflammatory habit of shooting people and razing villages. For example, in February, after militants killed 12 people in a dispute over a patch of land being surveyed for oil, the army launched a punitive raid on a town called Odioma, killing 16 people and destroying hundreds of homes. Such tactics help the militants recruit. At a recent rally, Mr Asari told locals that they might as well join his movement since the government would “victimize” them anyway.  The security forces are further compromised by the fact that some officers are no better than the gangsters they are supposed to be crushing. In January, two admirals were convicted of abetting the disappearance of a tanker carrying stolen oil.

In the south-eastern state of Anambra, government has ground more or less to a halt because of a quarrel between the state governor, Chris Ngige, and his political “godfather”. The tycoon who bankrolled Mr Ngige's election campaign is reportedly upset that, having been elected, Mr Ngige has not given him enough say in how the state is run.

For some reason, the police declined to intervene when, in November, thugs burned down the main government buildings in the state capital of Anambra and shot at the governor. This local crisis reflects badly on Mr Obasanjo, not least because the brother of Mr Ngige's “godfather” is a senior presidential adviser.

As if all this were not enough, Mr Obasanjo's opponents continue to challenge the results of the elections in 2003. Muhammadu Buhari, a former military dictator who was Mr Obasanjo's chief rival in the presidential poll, claims that there was serious rigging in 16 of the country's 36 states, including Anambra and Ogun, Mr Obasanjo's home state. Mr Buhari is suing to have the results overturned. Lower courts having rejected his suit, he is now taking it to the Supreme Court.

Mr Obasanjo's most ambitious promise, when he assumed office, was that he would fight the corruption that has kept Nigeria poor. To this end, he has appointed clever and energetic young technocrats to a number of key posts. The much-admired finance minister, for example, is struggling bravely to make public accounts more transparent, and to push a “fiscal responsibility act” through parliament.

By some accounts, graft has indeed retreated a bit. The anti-corruption chief, Nuhu Ribadu, went so far as to claim last month that whereas 70% of the country's oil revenues were being stolen or wasted two years ago, now only 40% were. He argued that central government was now much cleaner, but that certain state governors were still filching with gusto.

Whether or not Mr Ribadu's estimates are to be believed, his gripe about the states is justified. State governments raise very little cash themselves, but rely instead on oil money from the central pot. They swallow about half of this, spend it opaquely and howl at any attempt to impose fiscal discipline. The finance minister is trying to save some of the windfall from high global oil prices against the time when prices fall again; the government of Abia state claims that this is illegal and is suing for its share of the rainy-day fund.

Nigerians largely support the anti-corruption campaign, but some worry that Mr Obasanjo is too preoccupied with other matters to see it through. What is more, since he is barred from standing for re-election when his term ends in 2007, his power is sure to wane as that date nears.

His vice-president, Atiku Abubakar, would like to succeed him. Observers doubt that he would grapple effectively with corruption. The ruling party is split between the two men's supporters; the party boss who warned that the government was headed for collapse (and then resigned) is one of Mr Abubakar's allies.

Other contenders include some of the ex-dictators honoured on Abuja's street signs. That is a grim prospect. Earlier this month, a long-suppressed official report into abuses under military rule was leaked. It accused three ex-dictators of responsibility for unlawful killings, and recommended that none should be allowed to run for president again. One or two of them, however, probably will.