"It is a major blow to (Chinese President) Mr Xi's (Jinping) attempt to establish Chinese hegemony in the region and presents him with a fateful choice: embark on a dangerous escalation, or slowly and quietly back down," The Washington Post said in a lead editorial.
Noting that China's communist regime is reacting with rhetorical frenzy to the ruling by an international tribunal rejecting its expansive territorial claims in the South China Sea, The Washington Post said Beijing's insistence that the court decision is "invalid and has no binding force" only goes so far.
"Nations far beyond Asia will watch to see if the rising superpower violates a treaty it agreed to be bound by. If it does, the damage to China's international standing and influence could prove considerably greater than whatever it might gain from fortifying a few coral reefs," it opined.
The Washington Post warned that the United States must be prepared for the possibility that Xi will double down on his adventurism, perhaps hoping to take advantage of a president in his last months of office who has responded weakly to red-line crossings in other parts of the world.
"Any such action must be contested by the United States. The alternative would be to sanction Mr Xi's use of raw power to advance his nationalist aims - and open the way to serious conflict in East Asia," Washington Post reported.