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US President Barack Obama flies to South Africa on Friday to pay homage to his hero Nelson Mandela, who is fighting for his life in hospital.
Mandela's ill health means the two men, who shattered racial boundaries on either side of the Atlantic, will not hold a long-anticipated meeting for the cameras.
But reflections on Mandela's extraordinary journey from prisoner to president will permeate Obama's three-day stay.
Mandela, who turns 95 next month, was rushed to hospital three weeks ago with a recurrent lung disease.
On the eve of Obama's visit, South Africa's first black president was said to be in a critical condition, but had stabilised since a scare forced his successor Jacob Zuma to cancel a trip to neighbouring Mozambique.
"He is much better today," said Zuma after seeing Mandela on Thursday for the second time in less than 24 hours.
Yet South Africans, including Mandela's family, braced for the worst.
"I won't lie. It doesn't look good," daughter Makaziwe Mandela said. But "if we speak to him he responds and tries to open his eyes -- he's still there."
Obama, the United States's first black president, led a chorus of support for the man he called a "hero for the world".
Mandela's plight has lent a deeply poignant tone to the visit, around which Obama has built a three-nation Africa tour, and his plans could yet be disrupted by sudden developments in the ex-president's condition.
The White House says it will defer to the Mandela family and the South African authorities on any aspect of the visit that kicks off on Friday evening when Obama arrives.
"The president will be speaking to the legacy of Nelson Mandela and that will be a significant part of our time in South Africa," said US deputy national security advisor Ben Rhodes.
A visit by Obama to Mandela's former jail cell on Robben Island, off Cape Town on Sunday would now take on extra "profundity", he said.
Speaking in Senegal on the first leg of his long-awaited African trip, Obama described Mandela as "a personal hero".
"I think he is a hero for the world, and if and when he passes from this place, one thing I think we all know is that his legacy is one that will linger on throughout the ages."
The US president recalled how Mandela had inspired him to take up political activity, when he campaigned for the anti-apartheid movement as a student in the late 1970s.
The men met in 2005, when the former South African president was in Washington, and Obama was a newly elected senator, and the two have spoken several times since by telephone.
But there has been no face-to-face meeting between them since Obama was elected in 2008.
During his trip, Obama was also due to host a town hall meeting at the University of Johannesburg's campus in Soweto, the township where Mandela once lived, as part of the US president's Young African Leaders Initiative.
He will visit a community centre with fellow Nobel Peace laureate Archbishop Desmond Tutu and give a speech at the University of Cape Town.
But he will not be greeted warmly by all South Africans. "NObama" demonstrations were planned across the country by a coalition of leftist, pro-Palestinian and anti-drone groups.
The group planned to protest against what it described as the "arrogant, selfish and oppressive foreign policies" of the United States.
Meanwhile outside Mandela's hospital a wall of messages and flowers has become the focal point for a nation saying a long goodbye to one of the greatest figures of the 20th century.
"I came to pray for our father Nelson Mandela. We are wishing for our father to be fine," said Thabo Mahlangu, aged 12, part of a group from a home for abandoned kids who travelled to Pretoria.
Mandela has been hospitalised four times since December, mostly for a stubborn lung infection.
The man once branded a terrorist by the United States and Britain walked free from prison near Cape Town in 1990.
He went on to negotiate an end to white minority rule and won South Africa's first fully democratic elections in 1994.
He forged a path of racial reconciliation during his single term as president, before taking up a new role as a roving elder statesman and leading AIDS campaigner.
He stepped back from public life in 2004 and has not been seen in public since the football World Cup finals in South Africa in 2010.
But Mandela still draws vast global interest, interest which now appears to be wearing on his family.
Mandela's oldest daughter Makaziwe on Thursday slammed the "crass" media frenzy around her critically ill father, likening the press to vultures.
"They violate all boundaries," she said accusing the foreign press of "a racist element" by crossing cultural boundaries.
"It's like truly vultures waiting when a lion has devoured a buffalo, waiting there you know for the last carcasses."