Was the use of atomic weapons ever considered in Vietnam? Why/why not?
At the end of WWII, President Truman decided to drop the A Bomb on Japan--twice. He was confronted with this again in Korea. There were contingency plans produced that would have used atomic weapons against both the USSR and China during this conflict, but they were later shelved. Was the use of atomic weapons ever considered in Vietnam? Why/why not?
The use of nuclear weapons was considered a number of times in the Vietnam War. However, there is no evidence to show that any president ever came in any way close to actually using nuclear weapons in Vietnam. There are a number of reasons for this.
Your question seems to imply a comparison with World War II; if the US would use nuclear weapons in WWII, why not use them in Vietnam? The reason is that Vietnam was a very different war than WWII.
First, in WWII, no one had ever used nuclear weapons before. There was no public opinion one way or the other with regard to the use of such weapons. By Vietnam, nuclear weapons had become much more of a taboo. There was solid public opinion against their use in the US and in other countries.
Second, nuclear weapons would have been much less useful in the Vietnam War. In WWII, it could be dropped on cities that were at least relatively important to the Japanese war effort. By contrast, there were not really any cities that were important to the war effort of the Vietcong or even of North Vietnam. The North was not very industrialized and there was not really much in the way of targets for a bomb.
Finally, and perhaps most importantly, by the time of the Vietnam War, use of nuclear weapons might well have caused nuclear retaliation by the Soviet Union. In WWII, there was no danger in using nuclear weapons. In Vietnam, there was. The Soviets could have hit us with nuclear weapons if they wanted to do so in retaliation.
Thus, there was little benefit to using nuclear weapons in Vietnam and a great deal of danger in doing so. Therefore, their use was considered, but never very seriously.
I think that one can see there was a deliberation as to whether or not nuclear weapons could be used in Vietnam. At the point in which President Nixon understood the need for escalation before American troops could leave, Nixon spoke of using atomic weapons with Kissinger:
'I'd rather use the nuclear bomb,'' Mr. Nixon responded.
''That, I think, would just be too much,'' Mr. Kissinger replied.
''The nuclear bomb. Does that bother you?'' Mr. Nixon asked. ''I just want you to think big.''
President Nixon and his advisers understood that discussing the use of nuclear weapons would enhance the "madman theory" that was being posited at the time. This theory made clear that if the North Vietnamese did not report to the negotiating table in the hopes of ending the war, they would be subjected to an unprecedented offensive barrage. In seeking to get the North Vietnamese to negotiate the end of the war, Nixon "the madman" spoke openly about using nuclear weapons. The belief was that if the North Vietnamese believed that President Nixon would use nuclear weapons, it would convince them to begin the negotiation process. It was here where I think that the discussion of nuclear weapons can be seen in the Vietnam War.