First, some of the unjustifiable frustrations about "asymmetric" privileges to use the word N***** fall into the category of "manners" as Obama implied.
Second, people of a different complexion using the word among themselves privately are simply showing the hypocrisy of their racism, and their defensive affinity for "white identity." White Identity is a refuge for individuals collectively beset with some self-esteem problem.
There would certainly have been a time in our history when a survey of black citizens might prove that some unspecified number of black people secretly wished that they were white -- a reaction to the circumstances of oppression and social status. You would not find this feature among Caucasians. Did you ever hear a white person wish they were black, even as a matter of confidence between two of the same? Can you even imagine a white person with such a wish?
I'm totally opposed to the idea that we should censor Mark Twain's books which contain the word in a historical and cultural context, displaying exactly the same factors I've already mentioned. And in that "context," a further examination of Twain's works puts him in an enlightened and contemporary sphere 150 years ahead of his time. Take for instance the crime mystery "Pudd'n'head Wilson."
As a Caucasian, Trump's use of the word -- particularly in context of seemingly private conversation -- just demonstrates his lifelong racism. If he were to do it publicly, then we heap onto that the criticism for manners. But the mannerly thing to do is to avoid using the word at all, barring some exception to contexts that would make it inoffensive for those people to whom it applies as derogation.