How do the American people benefit from protecting Vietnam and the Philippines? Not to sound trollish, but I genuinely do not see why spending billions in the region and antagonizing China really helps us.
The US would never need to invade China in the (horrific) event of a conflict. Simply cut off their access to oil by blocking the Strait of Malacca. Better yet do nothing and allow Japan do it for you.
The United States has been pulling back from the world order since the end of the Cold War. We just don't need to engage with the rest of the world as much as we used to, especially now that we don't even need foreign oil (thanks fracking!). Trump is just continuing this trend with more bombast and directness, as is his style.