Mr James Mattis didn't wear a badge or uniform in Singapore over the weekend. There was zero doubt, though, that his role at the Shangri-La security forum was to play the good lieutenant to President Donald Trump's bad cop.
Mr Trump's abandonment of the Paris climate accord reminded world leaders there's a new sheriff in Washington, one who puts testosterone before evidence, bluster before reality.
The IISS Shangri-La Dialogue - named after its venue at the Singapore hotel, not the fictional utopia - trades in both hard security and soft reassurances. On Saturday in Singapore, US Defence Secretary Mattis sought to reassure a region reeling from "America first" policy moves.
"The United States," Mr Mattis said, "will continue to adapt and continue to expand its ability to work with others to secure a peaceful, prosperous and free Asia, with respect for all nations upholding international law."
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What about when bad-cop Trump doesn't respect the international community? Before scrapping the Paris agreement, Mr Trump spent a week in Europe shooting from the hip and alienating Germany, France and even tiny Montenegro. Nato partners are aghast at Mr Trump seeming to divide an alliance that has safeguarded peace for generations.
But here's the question Asia should be asking: What happens when the gunslinger/sheriff starts shooting in this direction?
And the shots could be both figurative and literal. On the campaign trail, remember, one of Mr Trump's biggest applause lines was threatening a trade war. For now, he talks less about China "raping" America or creating a climate-change "hoax", and more about cooperating on North Korea. But markets are never more than one early-morning @realDonaldTrump rant away from chaos. Mr Trump could easily tank currencies with a couple of foul-mood tweets on currency manipulation, 45 per cent tariffs or broader US travel bans.
Policymakers from Singapore to Seoul should brace themselves for the moment economic data starts to disappoint and an embattled president plays the blame game.
The US' trade surplus with Singapore may keep the latter out of the direct line of fire. Yet any actions against China and Japan would send shockwaves South-east Asia's way. And on a more basic trust level, Singapore is wise to be cagey with a president who arbitrarily scrapped a Trans-Pacific Partnership that the US initiated.
Actual shooting cannot be ruled out. Asia is awash with potential flashpoints: Beijing building military outposts on disputed islands; South Korea's Terminal High Altitude Area Defence missile defence system; the increasingly frequent North Korean missile tests; a drug war in the Philippines trying neighbours' patience; and confusion about Taiwan and the "one China" policy, among other issues.
And then there's Mr Trump.
Mr Mattis' speech was carefully parsed for hints of what a Trump doctrine might look like. Good-cop Mattis walked his beat with caution. The US welcomes Beijing's cooperation on North Korea, he said, but "friction" is a possibility. "While competition between the US and China, the world's two largest economies, is bound to occur," Mr Mattis said, "conflict is not inevitable."
Mr Mattis didn't say Mr Trump could just as easily be the aggressor, though it was written between the lines in bold font. The high point of Mr Trump's presidency so far was April 6, when he fired 59 Tomahawk missiles at Syria. It won him widespread applause and knocked the intensifying domestic probes into links between his campaign and Russia from the headlines.
Might Mr Trump wag the proverbial dog at Pyongyang to divert attention anew? Or perhaps face off with Chinese naval vessels in the South China Sea?
Sound fanciful? Last year, chief Trump strategist Steve Bannon said "there's no doubt" the US and China will go to war over the South China Sea within five to 10 years. Mr Bannon was removed from his National Security Council post in April but remains influential. Is it so far-fetched that a far-rightwinger with the ear of a thin-skinned president might accelerate the timetable?
Consider, too, that adviser Peter Navarro, author of the paranoid tome, Death By China, has Mr Trump's other ear.
Mr Trump's first budget proposal, meanwhile, requests US$54 billion (S$74.5 billion) of new defence spending, much of which will add US vessels and aircraft to Asia's increasingly crowded seas. That's on top of an already booming Asian arms race in China, Indonesia, Japan, the Philippines, Singapore, Taiwan, Australia and beyond. So much military hardware in such close proximity is inherently dangerous. Chinese and Japanese fighter pilots are facing off in the North Asian seas with bewildering frequency, while North Korean leader Kim Jong Un and Mr Trump seek to out-troll each other. What could go wrong?
So much for the utopian ideal of Shangri-La, eh?
• William Pesek, a Tokyo-based journalist, is a former columnist for Bloomberg and author of Japanization: What The World Can Learn From Japan's Lost Decades.