How hard would it have been to kill a king leading his troops into battle?

From Cryptonomicon

“Ronald Reagan has a stack of three-by-five cards in his lap. He skids up a new one: “What advice do you, as the youngest American fighting man ever to win both the Navy Cross and the Silver Star, have for any young marines on their way to Guadalcanal?”

“Just kill the one with the sword first.”

“Ah,” Reagan says, raising his waxed and penciled eyebrows, and cocking his pompadour in Shaftoe’s direction. “Smarrrt–you target them because they’re the officers, right?”

“No, fuckhead!” Shaftoe yells. "You kill 'em because they’ve got fucking swords! You ever had anyone running at you waving a fucking sword?”