In January 1966, Cooper accompanied Secretary of State Rusk and Ambassador W. Averell Harriman on an official visit to Philippine President Ferdinand Marcos as part of a widely publicized "peace drive". This visit, along with visits to South Vietnam in December 1965 and January 1966, reinforced Cooper's opposition to military operations in Southeast Asia. In a meeting with President Johnson on January 26, 1966, he again urged the president to forgo his announced intentions to resume bombing missions in North Vietnam and negotiate a settlement instead. Johnson was noncommittal, and that afternoon, Cooper returned to the Senate floor, urgently trying to convince the legislators that negotiation was preferable to escalation, even when it meant negotiating with the Viet Cong fighters in South Vietnam, which he believed was necessary to achieve peace. Cooper advocated a three-to-five-year cease fire, enforced by the United Nations, followed by national elections as prescribed by the 1954 Geneva Convention. Ultimately, Johnson did not heed Cooper's plea and resumed U.S. bombing missions in North Vietnam.