Most or all leftist journalists at the time blamed the killings on Nixon because of his incursion to try and stop North Vietnam army supply lines. Schanberg and other lefties tried to cover up for the commies in Cambodia. I doubt he could approach anything about Vietnam with an unbiased eye.
Is he? Didn't know that. But this story or account doesn't only come from him, does it? Aren't there lots of true-blue vets who say this about McCain's time at the "Hilton"?