Common to malignant narcissism is narcissistic rage. Narcissistic rage is a reaction to narcissistic injury (when the narcissist feels degraded by another person, typically in the form of criticism). When the narcissist's grandiose sense of self-worth is perceivably being attacked by another person, the narcissist's natural reaction is to rage and pull-down the self-worth of others (to make the narcissist feel superior to others).
How quick our President is to belittle those who dare disagree. You'd think he'd be much more to polite to one of his employers.