Barack Obama launched a long awaited week-long Africa tour in Senegal on Wednesday, aiming to fulfil neglected expectations for his presidency on a continent where he has deep ancestral roots.
But minutes after he landed in Dakar, it emerged that Nelson Mandela was on life support, as the anti-apartheid icon's apparent final days cast doubt over the shape of Obama's onward schedule in South Africa and Tanzania.
Obama stepped off Air Force One into the African night with his wife Michelle, and daughters Sasha and Malia, and is due to hold talks on Thursday with President Macky Sall, to highlight Senegal's solidified democracy.
His motorcade sped through streets cleared by police, as a local radio station played a musical arrangement of one of his 2008 "Yes We Can" campaign speeches, evoking better days for the increasingly under-pressure Obama.
In a highly symbolic moment for America's first black president, Obama will Thursday take a ferry to the House of Slaves on Goree Island, which memorialises hundreds of thousands swept into the Atlantic Slave Trade.
"A visit like this by an American President, any American President, is powerful," a White House spokesman told reporters on Air Force One, when asked about Obama's visit to Goree.
"I think that will be the case when President Obama visits and I'm sure particularly so, given that he is African American."
Obama's arrival in Africa came at a deeply poignant time as the world prepared to say a farewell to Mandela, who is gravely ill in a Pretoria hospital.
White House officials says they are monitoring Mandela's condition and praying for him, but his plight looks increasingly likely to complicate plans for Obama, who is due to spend the weekend in South Africa.
Napilisi Mandela, an elder in Mandela's clan, told AFP that the former South African president was on life support, and South African President Jacob Zuma called off a scheduled trip to Mozambique.
Obama and Mandela 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 the long awaited prospect of a public appearance between the first black presidents of South Africa and the United States is now impossible.
Obama, whose late father was from Kenya, claims a spiritual connection to Africa, but a crush of international crises in his first term thwarted his hopes to travel extensively in the continent. He did manage a short trip to Ghana in 2009.
His tour is designed to highlight Africa's emerging economic potential and growing middle class, as well as youth and health programs, and to emphasise US engagement in a region benefiting from a wave of Chinese investment.
"We are not too late," said Carney, pointing out that although Obama had been kept away, Vice President Joe Biden visited Africa in the first term, and there were also wide ranging diplomatic efforts by the administration on the continent.
But there has been disappointment in Africa, after Obama's 2008 election caused euphoria and an expectation that he would put Africa policy at the top of his agenda.
Obama hardly dampened expectations, declaring in Ghana in 2009: "I have the blood of Africa within me, and my family's own story encompasses both the tragedies and triumphs of the larger African story."
The current US president also travels in the shadow of his predecessors, Bill Clinton and George W. Bush, who are remembered fondly for their economic development and HIV/AIDS programs.
There is one glaring missing stop on Obama's itinerary: Kenya.
Officials said that the indictment of Kenyan President Uhuru Kenyatta at the International Criminal Court in The Hague, over previous election violence, made it politically impossible for Obama to stop by on this tour.
The president will be joined on Goree on Thursday by his wife, a descendant of slaves. Michelle Obama will also go to the all-girls Martin Luther King Middle School with her Senegalese counterpart.