Can the US President Act Like an Adult on his Asia Swing?

Good diplomacy doesn't make waves. Diplomats seek to achieve their nation's objectives by means short of war. In the modern era, they coordinate activities intended to enmesh other nations in a web of relationships that's so mutually profitable, so central to their own well-being, that war is unthinkable.

American diplomats preside over the broadest array of such activities, chiefly including trade relations, military, legal and intelligence cooperation, humanitarian and development assistance and a remarkably diverse portfolio of science and health objectives. Typically it's a low key, under-the-radar sort of business.

That's not President Donald Trump's style at all. He seems to enjoy making waves. He craves attention and despises detail. Supporting his 12-day trip to East Asia will test the mettle of five ambassadors and their staffs. That's not because they know Trump scorns their profession, but because at every stop there's ample opportunity for Trump to drop a clanger.

The American president's first stops are Tokyo and Seoul, two capitals already made jittery by his polemical exchanges with North Korea's dictator. In 1951, the US pledged to defend Japan in the event of an attack. In return, Japan pledged to forgo offensive military capabilities – a commitment manifested in its reliance on the American nuclear umbrella. In 1953, the US and South Korea reached a similar understanding. Sustaining the Korean and Japanese governments' confidence that the US would truly be willing to use its nuclear weapons to defend them has been a consistent objective of US diplomacy.

And now Trump, who has warned that North Korea "will be met with fire and fury'' if it attacks the United States with nuclear weapons but has conspicuously failed to remind Pyongyang that Washington is also pledged to defend South Korea and Japan. He has rattled the leadership of both allies. The lavish receptions awaiting him there may feed the US president's ego but are unlikely to leave them any more confident that he'll stand with them come what may from Pyongyang.

Perhaps Trump has learned a few things about the ordinary conduct of foreign affairs since his first foray abroad to Saudi Arabia and to the NATO headquarters in Brussels. Even so, the US president's repeated gaffes on that trip have fueled US diplomats' apprehension that at any time he may just wing it, improvising remarks that, if they don't cause a flap, at the least undermine his foreign peers' confidence in American constancy.

Put another way, senior leaders are expected to watch their words and control their impulses. Consider China's Foreign Minister Wang Yi, for example. Wang was in Hanoi last week, and just afterward (and with a straight face), a senior aide told reporters that Wang and Vietnamese representatives ''reached an important consensus. Both sides will uphold the principle of friendly consultations and dialogue to jointly manage and control maritime disputes, and protect the bigger picture of developing Sino-Vietnam relations and stability in the South China Sea."

Consider also Wang's principal interlocutor, Vietnamese Deputy Prime Minister Pham Binh Minh, whose press statement said he'd proposed that the two countries resolve disputes based on common sense and international law.

Neither Wang nor Minh were grandstanding, nor is peace about to break out along the infamous nine-dash line. In fact, the two officials were for the most part repeating a several year-old formula, one that's been of no perceptible utility in the resolution of the maritime disputes but, having been said again, has papered over recent unpleasantness, thus enabling the neighbors to get on with other business.

(Minh, however, took care to remind Wang of the relevance of international law, a pointed riposte to China's rejection of a tribunal's ruling that its infamous nine-dashed line is illegal.)

When heads of government go abroad, they function as diplomats. Like diplomats, they should leave politics and personal whims at home. If they can't behave constructively when matters of national security and prosperity are at stake, they are at least expected to behave predictably and prudently.

Trump hasn't yet shown that he's capable of coloring inside those lines.

David Brown is a retired US diplomat with wide experience in Vietnam and a regular contributor to Asia Sentinel.