News that the leader of the Nation of Islam, Louis Farrakhan, is seriously ill, has cancelled all appointments and temporarily handed over control of the organisation to an executive board, returns some longstanding questions to the fore. Namely: will the organisation survive him; if it does who will lead it; will the succession be peaceful; and, ultimately, is the Nation sufficiently relevant for any of those questions to really matter?

For those who wish to revisit other issues regarding his anti-semitism, homophobia or other transgressions, this posting is not for you. Not because such enquiries are not legitimate - I have pursued them myself more than once - but because they are not new and I doubt there is much new to say about them. More interesting is what Farrakhan's retirement tells us about the nature of black political leadership and the role the Nation has played within it.

In an open letter Farrakhan, 73, has called on his followers to "prove to the world that the Nation of Islam is more than the charisma, eloquence and personality of Louis Farrakhan ... is more than the physical presence of any individual ... "

The trouble is that like Elijah Muhammad before him Farrakhan has run the organisation in a manner that makes it virtually impossible for members of the organisation to do precisely that. When it comes to black nationalism the Nation looks more like post-coup Thailand - an absolute monarchy supported by a military dictatorship - than anything approaching a working democracy. There is little if any open debate in the organisation and all due and diligent deference must be shown to the leader.

"Minister Farrakhan is the Nation Of Islam," Arthur J Magida, the author of Prophet Of Rage: A Life of Louis Farrakhan and his Nation, told me when Farrakhan was last seriously ill seven years ago. "The Nation relies on his charisma, his organisational skills and his image as perhaps the most courageous and defiant black man in the United States. If he is sick, then the Nation is sick."

Just over a decade ago these talents were put to notable use with the million-man march - one of the biggest demonstrations in the nation's history. But, in a dilemma that has been felt within the anti-war movement over the last few years, these large numbers did not translate into anything lasting.

This is not a problem particular to the Nation. In the past, black American political culture has relied on a messianic tradition that came out of the church and that sits uneasily with large, democratically run organisations. It produces powerful leaders - such as Jesse Jackson, Martin Luther King, Malcolm X, Louis Farrakhan - but movements that rarely outlive them. When the leaders die or fall into disgrace the organisations they lead go with them.

Because of the unusual level of devotion demanded of Nation members these ruptures have, at times, been violent. As Malcolm X found to his cost it has little room for dissent (Farrakhan famously said Malcolm was "worthy of death" for leaving the organisation and publicly criticising its former leader Elijah Muhammad). When Elijah Muhammad died there was a spate of murders in the battle for succession. Whether any permanent handover of power will go a similar way depends on who emerges with the most political and material support once Farrakhan steps down.

Among the most likely contenders is Ishmael Muhammad, Farrakhan's assistant minister at the strategically vital Mosque Maryam in Chicago. Ishmael, the son of Elijah Muhammad, has been groomed determinedly by Farrakhan. Another contender is Leonard Muhammad, Farrakhan's son-in-law and chief of staff who has been the subject of numerous lawsuits following failed business deals. And finally there is Akbar Muhammad, who heads a mosque in Ghana.

Farrakhan's retirement would signal the exit of the last of a generation raised during a very particular era of black politics. Three years younger than King and eight years younger than X, Farrakhan also gained his political education in the years of civil rights and black power. A large proportion of the key players of that era were assassinated. Only Jesse Jackson remains as politically active and, while he retains a presence, he no longer commands the relevance and brokerage power that he did 20 years ago.

The episode of voter disenfranchisement in Florida following the 2000 election and the aftermath of hurricane Katrina, revealed a vacuum in black leadership at a national level. This lack of viable leadership and vibrant movement is not limited to African Americans. The entire American left has found itself wanting at these moments.

But it represents a certain generational moment among black Americans. In their place have come a smattering of African American individuals who have risen in politics not through religion and not necessarily with progressive views. The most prominent black politicians at present are Condoleezza Rice, Colin Powell and Barack Obama.

So whether, ultimately, it matters or not who leads the Nation depends in no small part on whether they can make it relevant. The constituency that the Nation most appeals to - disaffected and alienated black youth - exists in large numbers. But just because they are still there doesn't mean they want to keep on listening to the same old thing.