The sidelining of Robert Mugabe at the age of 93 after 37 years in power in Zimbabwe illustrates a growing problem – what to do with political leaders who will not or cannot depart the scene. Even at his advanced age, and having laid waste to the country's economy and agriculture and destroyed its currency, Mr Mugabe is still not ready to quit. He sees a continuing role as elder statesman.
Mr Mugabe is not alone in the world, and certainly not in Africa where five leaders have been in power for more than 28 years. In Russia, Vladimir Putin has been in power (as president for three terms and for one term as prime minister) for 18 years. He is expected to run for a further six-year term as president in March, bringing the total to 24. What will happen next?
Kremlin strategists are already plotting what kind of role he could have when his current two-term limit as president runs out. Perhaps a collective leadership? We do not know what Mr Putin thinks of this.
What is clear is that Mr Putin's dominance of the political scene has frozen politics in Russia in the last century. The parliamentary "opposition" are holdovers from the 1990s – the pro-Kremlin communist Gennady Zyuganov and the licensed jester Vladimir Zhirinovsky. They are like the mammoths preserved in permafrost that starving political prisoners in the Soviet Gulag would occasionally dig up. At least the mammoths could be eaten, whereas the old opposition is strictly decorative.
In the West the same problem exists but in a different form. With the voters' desire for a new face (or in the absence of young blood, a total outsider such as Donald Trump) the trend is for politicians to get to the top at a relatively young age. The poster-boy for the young and energetic politician is Emmanuel Macron, who reached the French presidency at 39, only to be beaten five months later by Jacinda Ardern, the New Zealand prime minister who won at 37.
What will Mr Macron do when he falls out of favour, as all democratic politicians do? The example of Tony Blair is instructive. As a politician of world-class charisma and persuasiveness, Mr Blair bewitched the British public when he came to power at the age of 44 but the terrible consequences of the Anglo-American invasion of Iraq and other missteps curdled the admiration into distrust.
The Labour party which he led to three election victories pretends he does not exist. Much of the rest of the country changes channel when he appears of television. But Mr Blair cannot stay away from politics. He has relaunched himself on a personal mission to reverse last year’s referendum decision to leave the European Union. While almost half the country would dearly love that outcome, he carries so much political baggage that he cannot be the man to lead the campaign except, perhaps, in the event of a national emergency of the scale which brought Winston Churchill back to Downing Street in 1940.
As for Barack Obama – who entered the White House at the age of 47 – what is he to do? It would be a shame for such an erudite man to follow the dignified if uninspiring silence of George W Bush, who has been devoting himself to painting.
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Richard Nixon, who left office in disgrace in 1974, spent the best part of 20 years prompting headlines of a comeback with trips abroad and well regarded speeches on foreign policy. It did not end well. In March 1994, on a trip to Moscow he was angrily snubbed by Boris Yeltsin. He died the following month.
The brutal truth is that a democratic politician will always struggle to escape the media narrative set by his or her opponents and an unforgiving press. David Miliband, the former British foreign secretary who was beaten by his brother Ed in a contest to lead the Labour party, writes that he had to keep silent on British politics after this sibling battle. "Anything I said was construed as a bitter attack on my brother, with the substance of my point obscured by alleged psychodrama," he writes in a new book, Rescue.
Mr Miliband has found a berth in New York, as head of the International Rescue Committee, an 80-year-old charity which helps refugees and displaced people all over the world. Clearly the United States is a place where a politician can make a new life for himself. Delving into the past, Helmut Schmidt, a great German chancellor, also found a suitable berth: after losing power he moved to the editor's chair at Die Zeit, a highbrow weekly publication which eschews the manipulative trickiness of most media.
But these are exceptions. The truth is that there are few good career paths for former leaders. Those that were lauded in power in western countries face contempt if they try to get back in the political game; dictators fear they could face vengeance at the hands of their own people or transnational justice, as in the case of Liberia's Charles Taylor, who resigned under international pressure and is now serving a 50-year sentence for war crimes.
Only one thing is clear: trying to bequeath the presidency to your wife as a means of hanging on to office in your dotage always causes a stink. This was the cause of Mr Mugabe's downfall. The prospect of "Gucci" Grace Mugabe as president brought the armoured cars on to the streets.
This is no academic question. In neighbouring South Africa, Jacob Zuma, the president and leader of the ruling African National Congress, is promoting his ex-wife, Nkosazana Dlamini-Zuma, to succeed him as party leader and eventually president. She has experience in government and as chair of the African Union, but critics see her candidacy as an attempt by Mr Zuma to stop investigators looking at his allegedly corrupt links with commercial interests. The ANC is to decide in a secret ballot later this month.