Calling this president of the United States a maniac is not uncivil; it is supported by facts.

Even by dictionary definition, Trump fits. He presents as a megalomaniac, full of "self-exaltation, passion for big things" (OED): "I know more about ISIS than the generals... Only I can fix it," etc.
He claims to be the male equivalent of a nymphomaniac: "When I see them I just can't help myself... when you're famous they just let you do it"

The more general meaning of "maniac" is someone who engages in wild, reckless, dangerous behaviour, like a maniac driver. 
China is a significant adversary, yet within days Trump unnecessarily pokes the Chinese on a matter of great sensitivity to them, Taiwan. 
The US needs support from the people of Iraq yet he has said repeatedly that the US should have taken the oil before leaving and if the opportunity should arise, the should not miss the opportunity to do so.

It is not uncivil to call a spade a spade when there is abundant evidence.