Hilsman continued to speak publicly, in print and on television, regarding what he thought should be done in Vietnam, such as in August 1964, when he warned against over-militarizing the conflict, and in mid-1967, when he said the war was not politically "winnable" and that the U.S. should scale down its military involvement and stop the ongoing bombing campaign against the North. He consistently maintained that had Kennedy lived, he would not have escalated the war the way Johnson did. Hilsman was an ardent supporter of Robert Kennedy's 1968 presidential campaign, serving as one of the expert advisors. He was part of a large "brain trust" of advisers to Kennedy during the crucial Democratic California primary in June 1968; that ended with another Kennedy assassination.