LYNDON B. JOHNSON: Assuming we do everything we can, to the extent of our resources, can we really have any assurance that we win? I mean, assuming we have all the big bombers and all the powerful payloads and everything else, can three Vietcong come in and tear us up and continue this thing indefinitely, and never really bring it to an end? That's one thing I want to look at. The second thing I want you to look at <...> can we really, without getting any further authority from the Congress, have all out support or sufficient, overwhelming support to work successfully, to fight successfully? <...> I don't know whether those men have ever thought, in making their calculations: One, whether we can win with the kind of training we have, the type of power. Ah, and two, I don't know whether they've taken into their calculations whether we can have united support here at home …
ROBERT MCNAMARA: I think Mr. President that, there are two thoughts on that. First, if we do go as far as my paper suggested, sending numbers of men out there, we ought to call up reserves. You have authority to do that without additional legislation. But I doubt that you would want to use it. Almost surely, if we called up reserves, you would want to go to the Congress to get additional authority. This would be a vehicle for joining together support. Now you would say, "Well, yes, but it also might lead to extended debate and divisive statements." I think we could avoid that. I really think if we were to go to the Clarks and the McGoverns and the Churches and say to them, "Now, this is our situation. We cannot win with our existing commitment. We must increase it if we're going to win, in this limited term that we define, in this limited way we define 'win,' it requires additional troops. Along with that approach, we are embarking upon or continuing this political initiative to probe for a willingness to negotiate a reasonable settlement here. And we ask your support under these circumstances." I think you'd get it from them under those circumstances. And that's a vehicle by which you both get the authority to call up the reserves and also tie them into the whole program.
I believe the above exchange implies even at that early date, McNamara never thought the Vietnam War was winnable except by using a very narrow definition of how winning could not be achieved, while he also proposed skirting critical debate.
My take on it is that McNamara is steering Johnson away from the American Peoples' best interests and toward those of the military industrial complex; of which former President Eisenhower warned against giving too much power whether "sought or unsought" in his farewell address.
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