The public esteems the Marines for their discipline and toughness. Like their bulldog mascot, Marines latch onto an enemy and don’t let go. They stand ready to fight in any clime or place — until recently.

A few years ago, policy-makers advocated a “pivot” to the Pacific, concerned that China was building forts on atolls in the South China Sea. The commandant of the Marine Corps immediately proclaimed a counter. Small groups of Marines would move into unoccupied islands in the South China Sea, after receiving permission from the host nations. From those islands, they could then fire missiles to sink …