Lyndon Johnson actually said...
Deep in our history is the memory of what President Abraham Lincoln said to his countrymen in the dark days of 1861: 'Suppose you go to war, you cannot fight always; and when, after much loss on both sides, and no gain on either, you cease fighting, the identical old questions as to terms of intercourse are again upon you.'
Context
Toasts of the President and Prime Minister Maiwandwal
03/27/1967