Dar es Salaam - Africa is a home from home for American presidents, as they repair or polish political legacies, drawn by a continent's palpable needs and explosive economic potential.
The idea that leaders leave behind works that endure was a constant theme of President Barack Obama's Africa tour, which ended in Tanzania on Tuesday, and was shadowed at every step by the plight of Nelson Mandela.
Obama puts the anti-apartheid icon on a pedestal alongside Mahatma Gandhi, George Washington and Martin Luther King, proclaiming the political legacy his hero can no longer voice as he lies in hospital.
"Mandela's spirit could never be imprisoned - for his legacy is here for all to see," Obama told a diverse audience of young people, "black, white, Indian, everything in between" in Cape Town.
"Nelson Mandela showed us that one man's courage can move the world," Obama said, using the moral fight against apartheid to inspire a rising generation to fix their own corrupt political cultures.
After standing in a quarry where Mandela broke rock watched by guards, and in the tiny Robben Island cell where he dreamt of emancipation, Obama also seemed to draw strength for his own political project.
The idea that one person can change the world with bottom-up activism is deep in Obama's political soul and helped sweep him to the presidency in 2008.
Yet Obama's contention that "we are the change we seek" often slams headlong into entrenched interests and political division in Washington, and the indifference of great power politics on the world stage.
American presidents have long seen Africa as a place to burnish a questionable legacy, or to sate their political yearnings once they leave office.
Jimmy Carter has worked for democracy and public health on the continent in a post-presidency that is more successful than his four White House years.
Bill Clinton is remembered for the Africa Growth and Opportunity Act (Agoa), a cornerstone of US investment and engagement.
In retirement, Clinton brokered deals between US drugs giants and developing states that widened access to life saving treatments.
George W Bush, pilloried for anti-terror and economic policies elsewhere, is remembered as a humanitarian in Africa for an HIV/Aids and malaria programme that saved millions.
Obama praised the scheme as Bush's "crowning achievement" then came face to face with his predecessor in Tanzania, in Africa to work with his policy institute.
Questions of whether his Africa legacy will pale against that of Bush, seemed to irritate Obama during his tour and South African President Jacob Zuma rode to his rescue at one point.
"I always avoid to talk about legacies of people who are still there, generally," Zuma quipped, drawing a grin from Obama.
But talk of legacies always gathers around second term US presidents who often look abroad as their power ebbs at home.
"Let me just say that I'm going to be President for another three-and-a-half years," Obama reminded people in Soweto.
Son of a Kenyan
"One of the things that you learn as President is not only do people want you to fulfil your promises, but they want you to fulfil your promises yesterday."
That expectation in Africa is a particular burden for Obama, as the son of a Kenyan and as America's first black US president.
A crush of international crises, and an austerity crunch in Washington, has meant there has neither been the time, nor the financial resources available to Bush and Clinton, for Obama to lavish on Africa.
He did unveil a $7bn dollar bid to leverage private investment to spread electric power in Africa, a new trade initiative, fresh health programmes, a $10m effort to protect Africa's wildlife and food security efforts.
For all his inspiring rhetoric, Obama's role in Africa may be more prosaic than that his predecessors, and involve reauthorising Agoa and evolving Bush's Pefpar, rather than coming up with splashy new programmes.
And his new initiatives will unfold over many years.
"Ultimately the goal here is for Africa to build Africa, for Africans," he said, emphasising the need to build local capacities not just hand out aid.
All of which, plus hints by Obama that he will mount another Africa tour before leaving office, suggests that legacy in the continent remains to be written.