you're missing the point - he has claimed, over the years, that an evil Republican president sent him to Cambodia at the height (low) of his four month tour of combat duty in Vietnam and the president (at that time, whomever) lied about the fact he was there. He's said this experience was "seared into" his soul. Now he either admits that Nixon wasn't president then, in which case the whole base upon which his history of political posturing has been based, is removed. Otherwise he tries to obfuscate and say that it was beloved liberal hero LBJ who was the dastardly one who lied and so molded him. In any event it bears prudence to the fact the whole story is a LIE and it's underpinning all his other claims which then crash like a house of cards on any subsequent scrutiny.
When did he say Nixon sent him? I have heard that, but haven't really followed this aspect of the story much.
If true......blockbuster stuff.