From a May 23, 2013 Esquire article by Tom Junod:
Sure, we as a nation have always killed people. A lot of people. But no president has ever waged war by killing enemies one by one, targeting them individually for execution, wherever they are. The Obama administration has taken pains to tell us, over and over again, that they are careful, scrupulous of our laws, and determined to avoid the loss of collateral, innocent lives. They’re careful because when it comes to waging war on individuals, the distinction between war and murder becomes a fine one. Especially when, on occasion, the individuals we target are Americans and when, in one instance, the collateral damage was an American boy.