Yes, it is mental illness, thanks to the leftist media. There is a bill in the works to study this ailment. I know of several severely afflicted. 

https://www.libertynation.com/trump-derangement-syndrome-isnt-just-a-pejorative-term-anymore/

from the article:

"Victims of TDS usually appear ready to defend the indefensible, align themselves with the worst of humanity, and move their own ethical and moral goalposts at any time – all for the sake of opposing Trump’s position on every issue.

There are countless examples of journalists, television news anchors, and talk-show hosts directly contradicting their own previously stated opinions just so they can criticize the president.

Renowned psychologist Alex Pattakos, Ph.D., writing in Psychology Today – a couple of months before Trump won his second White House term – described Trump Derangement Syndrome as “a form of toxic criticism and negative reaction to former President Trump’s statements and political actions.” Pattakos went on to observe:

“Signs of TDS can be observed along a continuum of reactions, ranging from verbal expressions of intense hostility toward President Trump to overt acts of aggression and even violence against anyone supporting or anything symbolizing him.”