In the late 60's, Presidential candidate Richard Nixon said he had a "secret plan" to end the war. This eventually seemed to involve the bombing of Cambodia and the pursuing of Viet Cong across the borders. Why did this strategy not work?
There are a number of reasons why Nixon’s “secret plan” did not work. Let us look at three important factors.
First, Nixon’s plan came too late to do any good. Let us assume, for the sake of argument, that his aggressive bombing campaign would have been effective earlier in the war. By the late 1960s, the Vietcong and the North Vietnamese had so much momentum built up, and the South Vietnamese regime was so discredited, that simply bombing safe havens in Cambodia could not do much to strengthen the South and weaken the communists.
Second, Nixon’s plan was accompanied by a reduced American presence. Nixon was not bombing and following it up with aggressive moves by the ground forces. Instead, he was “Vietnamizing” and withdrawing American troops. This meant that there was no way that the US could follow up on the success, if any, of the bombing.
Finally, public opinion in the United States was too far gone by this point. Americans had turned rather solidly against the war. Nixon could not possibly have gotten Americans to support an expanded, or even a continued, war in Vietnam.
Thus, Nixon’s “secret plan” might have worked in 1965, but it could not work by 1969.