I am reminded of Herman Wouk’s book,” The Winds of War.” and the way that FDR reach down into the ranks and found experiences officers to give him advise. Pug Henry was a composite of several such men. I wonder of Lyndon was capable of employing such men. He seemed to favor sycophants, guys like Bill Moyers.
Of course Viet Nam was a mistake to him because he made the mistake of not winning it. Early on the war had great public support and by the Johnson-McNamara system of engagement lost that.
IMHO, The Viet Nam conflict drained the Soviet treasury, therefore robbing them of the ability to build their own defense. The Johnson-Mac team is due given some sort of credit for keeping our strategic military strong. If the USA had decent intel on the USSR at the time I'm quite sure they would have sacrificed a lot of our global ability.