Barack Obama touches down in Japan on Wednesday to start an important week-long trip that will also take in three other countries: South Korea, Malaysia and the Philippines. His overriding goal will be to reassure these allies about enduring US commitments, while sending a clear message to neighbouring states, including China, about US intent to maintain its Asia-Pacific pivot.
This is a simple but crucial message at a time of significant geopolitical turbulence and tension - both in the region and beyond. The trip, for instance, comes when US foreign policy attention remains diverted by events in Ukraine, which many in Asia are also watching closely as a potential signal for how Washington might respond to any future Chinese belligerence.
However, the need for US reassurance comes in a broader context of the postponement of Obama's planned Asian trip last autumn during the US government shutdown. There has also been substantial regional change in the past 18 months, which has seen a once-in-a-generation transition of leadership in China, the subsequent rise of a more assertive Beijing, plus the election of the conservative, nationalist Japanese prime minister, Shinzo Abe.
The fluid, unpredictable environment this has generated has caused continual headaches for Washington since Obama was re-elected in 2012.
Indeed, the president currently faces the most significant array of obstacles towards realising his goals in the Asia-Pacific region than at any other time during his presidency. For instance, progress towards securing the landmark Trans-Pacific Partnership agreement may be stalling, despite Washington's ambition to secure a deal this year featuring at least 12 countries that collectively account for around 40 per cent of the world's gross domestic product.
Moreover, there are significant bilateral tensions, including between Japan and South Korea (Washington's two leading regional allies), which Obama is fire-fighting. Only last month, he made some potentially important progress in this regard at the Nuclear Security Summit in The Hague, where a three-way meeting with Abe and South Korean President Park Geun-hye was the first high-level contact between the countries for months. As in much of East Asia, underlying bilateral tensions between Seoul and Tokyo reflect the legacy of a troubled past. In this instance, significant distrust and anger remains from the period when Korea was under Japanese rule, including as an annexed colony from 1910 to 1945.
These issues have been given new impetus by the election of Abe, whose conservative, nationalist agenda emphasises greater pride in the country's past, and also overturn remaining legal underpinnings of the country's post-second-world-war pacifist security identity, so that it can become more actively engaged internationally. While this is all largely aimed at countering Beijing's growing power, it has alarmed Seoul, too.
Of course, these deep-seated problems are not ones that Washington can fully resolve quickly, but careful management of them is key to realising US objectives. In both Tokyo and Seoul, Obama will thus stress the importance of enduring US partnership with each country, including against aggression from external parties, while continuing to promote a common trilateral agenda, including towards the North Korea nuclear threat. Obama's agenda in Malaysia and the Philippines, two key members of the Association of Southeast Asian Nations, will also centre on strengthening alliances. And, once again, reassurance is key, given regional concerns that US interest in Southeast Asia could dwindle if its relations with China improve significantly.
There is currently considerable distrust of China within many Asean countries, not least over territorial and natural resource claims in the South China Sea. Late last year, for instance, Beijing refused to participate in a UN arbitration process over a territorial conflict with the Philippines.
In this context, Manila is keen to strengthen ties with Washington, and this is expected to be formalised with the signing of a bilateral defence co-operation treaty during, if not before, the trip. This will reportedly enable greater rotation through the country of US ships, sharing of local bases, and aircraft and troops.
In Malaysia, Obama will be the first US president to visit for some 50 years, and the moment is opportune with Kuala Lumpur assuming the Asean chair next year. He is likely to find his hosts particularly welcoming, in light of the recent deterioration in relations with China since the disappearance of Malaysia Airlines Flight 370.
Taken overall, the president has a clear and substantial agenda in each country, but his overarching ambition will be to provide reassurance about enduring US commitments to the region on the security, economic and political fronts.
Moreover, with a deal on Trans-Pacific Partnership still uncertain, Obama may be able to unlock key issues to advance what would be a potentially game-changing agreement cementing US influence in the region well beyond his presidency.
Andrew Hammond is a former UK special adviser in the government of Tony Blair, and an associate at LSE Ideas at the London School of Economics