Barack Obama’s sojourn in Kenya, the land of his father, was akin to the climax of a classical odyssey or epic saga. After un-numbered African generations suffer the agonies of enforced servitude and historical exile, a favoured son, blood of their blood, returns in triumph to claim the mantle of leader and heroic figure. Doubtless, White House spin doctors would love to have the story told this way. Yet notwithstanding the tired cynicism of the political age and the familiarity of Obama’s much-told personal journey, this remarkable reversal of fortunes, briefly glimpsed and savoured this weekend, remains genuinely uplifting.

Symbolism does not feed starving children. Obama’s agenda in Nairobi, and subsequently in Addis Ababa, home of the African Union (AU), illustrated both the reach and the nitty-gritty limits of American presidential power. Interviewed by the BBC on the eve of his trip, Obama teetered on the brink of complacency. Like the university lecturer he once was, he long ago identified Africa’s principal challenges: lack of good governance and transparency, weak institutions, corruption and, of course, widespread, entrenched poverty, malnutrition and avoidable disease. More than six years after he entered the White House, these problems persist. Some may even have worsened.

This is not Obama’s fault. Too often, the international community looks to the US to solve all its problems. It should have learned by now how fallible Washington’s supposed solutions can be. But could Obama, as the leader of the world’s wealthiest and most powerful nation, have done more, more quickly and more effectively, to help address these issues in recent years? Some African commentators answer with a resounding “Yes”. Obama’s current emphasis – encouraging indigenous, home-owned economic development and entrepreneurship as an alternative to dependence on foreign aid and assistance – is fine as far as it goes.

But it is hard to escape the wider, strategic and regional context. This daunting backdrop includes largely unaddressed instability in eastern Democratic Republic of Congo and the Central African Republic; anarchic, atrocity-strewn civil war in South Sudan; festering Islamist terrorism in Somalia, Mali and northern Nigeria; and unfettered, US-tolerated dictatorship and corruption in Zimbabwe, Mozambique and Angola. The resulting human toll across sub-Saharan Africa, compounded by a lack of strong AU collective leadership and ongoing, endemic under-performance in education, healthcare, disease prevention and gender equality is an affront to the conscience of the world. Obama eloquently voiced his opposition to Kenyan attitudes on gay rights in his press conference yesterday

Obama could and should do better. And now is the optimum moment for him to try. He has 18 months left to go in a presidency that has hit a Republican roadblock in Congress in terms of domestic legislation. The president’s bitter regret over his failure to enforce tougher gun controls, an issue about which he cares passionately, is a doleful measure of the limits on his capacity to act at home. But like previous White House incumbents nearing the end of a second term, Obama simultaneously enjoys great freedom of action in international affairs, an area where Congress’s writ mostly does not run. With yet another Bush clan member prospectively measuring the Oval Office curtains, the rare opportunity that now presents itself must not be missed.

Africa aside, Obama has already demonstrated awareness of this golden chance to put turn fine ideas into tangible realities. The long overdue, welcome US rapprochement with Cuba, sealed this month by a raising of flags in Washington and Havana, is a good example of what can be achieved. Now the gulf between the two has at last been bridged, it will be all but impossible to go back. Likewise on Iran, Obama fully grasped the long-term, positive implications of a nuclear deal with Tehran, and the highly dangerous, likely consequences, should negotiations fail. Hardliners in both countries (and Israel) will do their best to wreck the pact. But in an important sense, they have already lost the argument. A psychological barrier has been smashed. Iran and the US are talking again. It’s the new normal.

The trick now is to project Obama’s passion for connection into strategic and human advances elsewhere. American historians who like to partition time into eras may one day dub the Obama era “the age of engagement”. And more effective US engagement is now badly needed on a range of fronts including, for example, Syria and Russia, if the recent, sharp deterioration there is to be arrested. Obama started his time in office promising to “reset” relations with Moscow. But the aggressively nationalist recidivism of Vladimir Putin, manifest most obviously in last year’s brazen theft of Crimea, cooled his ardour. The “new Cold War” is too important, and too threatening, an issue to leave dangling. A big push to defuse east-west tensions is required.

Much the same may be said of China where, during Obama’s watch, a domestically repressive and internationally expansionist leadership clique, led by President Xi Jinping, has taken unchallenged charge. The recent arbitrary round-up of human rights lawyers and activists mirrors Beijing’s illegal attempts to extend control over the East China and South China seas.

Obama’s so-called “tilt to Asia” has been more of a wink and a nudge so far. As internal economic, financial and social strains trigger increased Chinese external assertiveness, Obama must work harder to engage Beijing – and to convince hard-line factions that he is not merely a fine public speaker with interesting family roots.