Later presidents would prove less responsive to a committee whose recommendations were sometimes at odds with administration policy. President ­Kennedy embraced the advisory system he inherited from Eisenhower, but conflict between the Johnson administration and PSAC over such issues as the antiballistic­-­missile program, supersonic transport, and the conduct of the Vietnam War caused the committee’s influence to wane. Donald F. Hornig, science advisor during this period, explained:

There is nothing sadder than an adviser whose advice isn’t wanted. During World War II and at the time of Sputnik, there was a clear identity of interest between the scientific community and the President. The President knew he needed advice, and the country knew he needed advice; and under Killian a heroic role was played. As time went on, quite aside from the building up of scientific expertise in the Department of Defense, attentions turned to other things; the most urgent political items were no longer quite so closely allied with the things PSAC was interested in. And in fighting its own personal battles, PSAC came to be regarded, rightly or wrongly, as having its own political positions.

Goodwill eroded to the point that Nixon felt the committee could best serve his interests by ceasing to exist. A science advisory committee, in modified form, was restored under President Ford, and every president since has at least given the appearance of having expert scientific advice at his command, but the influence PSAC wielded at its height has never been equaled. It was a unique set of historical circumstances that established the “identity of interest” Hornig described. And it was also a special collection of people, Killian recalled, who were able to serve two such demanding masters–­science and the president–simultaneously:

This group of science advisers had a deep sense of responsibility to science, along with an unshakable faith in its importance both to the individual and to the nation. They loved science and wanted others to share their enthusiasm for it and to discover its inner power to make men and women a little more creative, a little more civilized, and a little more humane.