The U.S.’s Delicate Balancing Act in the South China Sea | TIME

For years, China has been testing the limits of its aggression in the South China Sea to see how much it can push before someone, meaningfully, pushes back. It’s a dangerous game that recently left three Philippine Navy personnel injured after their resupply ship to the Second Thomas Shoal—an atoll at the center of disputes over rival territorial claims of the all-important waterway through which a third of the world’s trade passes—was surrounded and fired upon with a water cannon by Chinese coast guard and militia vessels.

In video of the March 23 incident, crew members could be heard shouting as jets of water pummeled the Philippine ship, which sustained heavy damage.

CAUGHT ON CAM: A GMA Integrated News Exclusive: “Tama na, Lord!” Horror as China Coast water cannons Philippine resupply ship @24OrasGMA @gmanews pic.twitter.com/rUIKi8ws8O

It’s not the first such attack by Chinese forces on Philippine sailors, nor is it likely to be the last. But looming over the increasingly confrontational encounters between the two nations is the potential of future U.S. military involvement. A mutual defense treaty between Washington and Manila necessitates one to come to the support of the other in the case of an “armed attack”—though it remains unclear what exactly would constitute such. “Responding to coercive actions in the ‘grey zone’ is difficult precisely because the lines between peace and conflict are blurred,” says Veerle Nouwens, executive director for Asia at the International Institute for Strategic Studies.

So far, China’s actions have only elicited sharp diplomatic protests. After the weekend incident, the Philippines summoned a Chinese diplomat to condemn “the aggressive actions by the China Coast Guard,” while the U.S. State Department reaffirmed its support for the Southeast Asian country, with a spokesperson saying China’s actions “are destabilizing to the region and show clear disregard for international law.” China’s defense ministry, meanwhile, called the Philippines a provocateur, warning that it should “cease making any statements that may escalate tensions and stop all acts of encroachment.”

Whether the war of words could one-day morph into an actual