The current US president has made it very clear that he will do whatever necessary to ensure that China will not rise to gain more power over the United states, whether economically or otherwise. Should china take control of protecting the sovern lands in the South Pacific, the US will not step away without a fight.
China is flexing its muscles to test its power under the Trump administration. Trump and the United States need to make sure that Russia is told no. First it is just these islands but the next day it could be China trying to take Hong Kong over or something worse.
The USA is entering an era of confrontation. The Trump administration, in trying to rip up trade agreements and dismantle obamacare, has bitten off quite a bit. They will have fights at home and abroad so it seems that lands in the South Pacific will not be at the top of their battling agenda.
The U.S. is not foolish to start war with China because China is also a powerful nation that is well able to fight back. When China says it will protect sovereign lands in South Pacific, they are simply daring America to try and stop them. We are no longer the super power, other nations have the military prowess that we once boosted of.