During the Vietnam war, what options were available to president Johnson and Nixon? What were the advantages and disadvantages?

When South Vietnam was in danger, Johnson initially sent the Marines and paratroopers to protect the American installations. Some advisers, like Undersecretary of the State George Ball and McNamara recommended to the president to "expand promptly and substantially" the U. S. military in South Vietnam. Since Johnson didn't want to lose Vietnam to the communists, he decided to accept McNamara's recommendation which led to a massive escalation of the war. If they went for the negotiation and see hesitations of the communists to negotiate may only mean that they are nearing victory in South Vietnam.