They are utterly dependent on the Freedom of Navigation enforced by the US Navy. While their economy is dependent on many things it is most starkly illustrated in their dependence on oil and their inability to safeguard its arrival in China against even a fourth tier force within reach of its tankers.
Click image for a HUGE version. 
They know full well what we can do to them if we are pushed too hard. We wouldn't even need to fire a shot.
SpyNavy
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)