When the Permanent Court of Arbitration in The Hague ruled last July against expansive Chinese territorial claims in the South China Sea, Beijing's strategy to dominate its backyard appeared to be in disarray. Politicians in Washington sought vainly to hide their triumphalism.
But, in hindsight, that was the high point - or low point, depending on your perspective - in the struggle for dominance over the crucial waterway, through which about US$5 trillion (S$7 trillion) worth of seaborne trade flows each year.
Since then, the US has suffered setback after setback in its efforts to rally other countries with competing claims in the region, while China has accelerated its militarisation and construction of artificial islands that give it effective control of the territory. Even some US officials privately acknowledge that China has won the battle for the South China Sea without firing a shot.
In the annals of American decline, this episode will surely loom large.
Mao Zedong, the peasant guerilla fighter who ruled China for 27 years, once described the US as a "paper tiger": fierce in appearance but ultimately harmless. The waterway debacle has lent credence to those in Beijing who adhere to this view today.
Much of the fault lies with Mr Barack Obama, the former US president, and Mrs Hillary Clinton, his secretary of state. President Donald Trump and his administration are in danger of accelerating the slide in American credibility.
From around 2011, the Obama administration recognised China's rise as the defining challenge to US predominance in the world and explicitly sought to "pivot" from grinding wars in the Middle East towards the projection of power in the Asia-Pacific. This made even more sense as the shale oil revolution at home reduced US reliance on Arab oil.
But, by the time the "pivot" was quietly rebranded as a "rebalance" after several years of inaction, it became clear that the policy had been an unmitigated disaster. Not only did it deeply antagonise Beijing and give the ruling Communist Party an excuse to expand its aggressive territorial claims, it also left allies in the region seriously doubting America's capabilities and resolve.
China and those allies took careful note of Russia's seizure of Crimea and incursions into eastern Ukraine as well as Mr Obama's quickly abandoned "red line" over the use of chemical weapons in Syria.
In the wake of these and many other perceived capitulations, Beijing accelerated its island-building and militarisation in the South China Sea. In the past three years, it has added more than 1,300ha of land - nearly 10 times the size of London's Hyde Park - on seven reefs and outcrops and installed runways, ports, hangars, radar and weapons systems.
This has been combined over the past year with a robust and highly successful diplomatic effort to convince neighbouring countries to tilt away from Washington and embrace Beijing.
The most spectacular example has been the former US colony of the Philippines, where President Rodrigo Duterte has "said goodbye" to America and all but sworn allegiance to China.
Apart from Taiwan, the self-governing island that China maintains is its territory, all the other claimants to parts of the South China Sea - Malaysia, Vietnam and Brunei - have moved closer to Beijing since last July's arbitration ruling.
Mr Trump is too distracted by controversy and Twitter battles at home to pay attention to or understand the complex evolving situation in the South China Sea. His appointees, such as Mr Rex Tillerson as secretary of state, have only exacerbated the recent legacy of US indecision by talking tough about curbing Chinese expansionism and then backtracking.
The continued US insistence that it wants only to ensure freedom of navigation in the South China Sea is somewhat disingenuous because what it really means is freedom for its spy ships and aircraft to conduct surveillance operations along the mainland Chinese coast.
That is something the US would never accept and it should now be up for negotiation. Vainly hoping that China will dismantle its artificial islands and return to the status quo ante is untenable.
Washington needs to acknowledge the reality of Chinese military supremacy in the waterway and work out an accommodation, involving all interested parties in the region, that avoids an accidental slide towards war.
This would certainly be a geostrategic win for China but it might also allow the US and other countries to convince Beijing that its 19th-century views on territorial expansion and great power relations are outdated and illegitimate.
In making the argument against China's creeping neo-imperialism, the US could remind the country's leaders of the words of Mao who said, "Imperialism will not last long because it always does evil things", and imperialists always end up as "dead tigers".