It is true that US sea power could block Russia and China from conducting trade in large parts of the world. But that would be an overt act of war. It is certainly something to watch for, but I don't think we are very close to that point yet, and certainly not against China. And, were the USA to get into a war with China it could be very dicey for Japan, the Philippines, Singapore, Malaysia, etc. Power over the sea ways can be exercised from air bases as well as from the deck of a carrier. Japan could start having problems importing fossil fuels, for starters. Which way would Vietnam go? How secure would the new US access to Philippine bases be? I sincerely do not want to find out.    

"It is not necessary to have hope in order to persevere."