One must disagree. How many times has Trump - senior, junior, et al, been exposed to the obligation of "o-a-t-h". "I swear to tell the truth, the whole truth, and nothing but....".
There is almost a magic, at least an alchemy in these words. It demands - and reasonably, morally expects - of those who say the words to dismiss, to reject abjectly, lies and, yes, half-truths that are more devious than outright lies. These words spoken and declared sacred impel the person to search their memory, their intelligence, in conscience the "wholeness" of declaration. 
Whether in compliance or in the breach, these essentials of truth permeate, not only the courts of law, litigation but common civil discourse, friendship, family, that is society at large.
Donald Trump Jr. understands better than most, I suggest, the implications of truth, the whole truth and the adjustment, skill and advantage - for some - that allows them to lie and dissimulate with impunity, along with the effects on others.