What is your solution?
Lend-lease. Finance, arm and train China's neighbors, but stay out of it while continuing to provide a nuclear umbrella to prevent China from engaging in nuclear blackmail (since none of China's South China Sea neighbors have nukes). Once we're out of Afghanistan, some of the $100b we spend annually there can be diverted towards interest-free loans for China's neighbors, to be spent on American weaponry that will bring them up to par with China's armory.
I think direct American intervention should be highly conditional and require regional players to pony up significant forces and/or money. Saudi Arabia, Kuwait, Germany and Japan covered the entire cost of Desert Storm. Much like Desert Storm, any American intervention in SCS should be predicated on the strong-arming of all interested parties for either money or significant military participation. Otherwise...
I understand that a lot of people think our participation in WWI and WWII, where we lost 500,000 men, only to be jeered by the Brits for being “late” to the festivities, set the pattern for posterity regarding an aggressive American posture towards big wars far from our shores. It has to be said however, that our 19th century forebears seem not to have been particularly concerned that they missed out on the Napoleonic Wars, the Franco-Prussian War, the Crimean War or any of the other big wars fought in Europe during that era.