Not plausible or even possible; He IS mentally ill.  He has very obvious, pervasive signs of Narcissistic Personality Disorder,  which is considered a mental illness by psychiatrists, DSM-V.  to those of us who are trained, it is very clear.  To the general population, it's easy to think that he means what he says, to write off the instability, and immaturity;  but to a trained eye, it's easy to recognize a pattern of grandiosity, self-inflation, hypocrisy, and lying.