This op-ed by 2014-15 visiting fellow Kirk W. Johnson was originally published in The New York Times. LOS ANGELES — "Let's be perfectly coldblooded about it," President Richard M. Nixon mused to Henry A. Kissinger. "South Vietnam is probably never gonna survive anyway." It was August 1972, and Nixon was worried about the inevitable collapse of South Vietnam after American forces withdrew. Mr. Kissinger concurred: "We've got to find some formula that holds the thing together a year or two. If we settle it, say, this October, by January '74 no one will give a damn." This formula became known as……