...The
Kennedy administration was disturbed by what they considered "blatant Chinese communist aggression against India". In a May 1963
National Security Council meeting, contingency planning on the part of the United States in the event of another Chinese attack on India was discussed.
Defense Secretary Robert McNamara and General
Maxwell Taylor advised the president to use nuclear weapons should the Americans intervene in such a situation. McNamara stated "Before any substantial commitment to defend India against China is given, we should recognise that in order to carry out that commitment against any substantial Chinese attack, we would have to use nuclear weapons. Any large Chinese Communist attack on any part of that area would require the use of nuclear weapons by the U.S., and this is to be preferred over the introduction of large numbers of U.S. soldiers."
[60] After hearing this and listening to two other advisers, Kennedy stated "We should defend India, and therefore we will defend India."
[60][61] It remains unclear if his aides were trying to dissuade the President of considering any measure with regard to India by immediately raising the stakes to an unacceptable level, nor is it clear if Kennedy was thinking of conventional or nuclear means when he gave his reply.
[60] By 1964 China had developed its own nuclear weapon which would have likely caused any American nuclear policy in defense of India to be reviewed.
[60] ...
https://en.wikipedia.org/wiki/Sino-Indian_War