“An exorcist might call it ‘partial possession’ or ‘demonic infection.’”
Never heard of “demonic infection”. But I believe the possession in these people is not partial; it’s 100%. It would be like being partially pregnant.
The demons are laying low so as not to scare too many people. If KJP’s head were to spin and spew vomitus, it would have people running to the nearest exit, and they must have people listening.
Many people around us are not fully possessed or they would be completely dysfunctional at times (nail-spitting, levitating, foaming-at-the-mouth, wall-climbing dysfunctional).
BTW, the opposite end of the possession continuum is NOT demonic oppression. Oppression is an external influence on the mind, body, and soul of a non-possessed person.
Ignore, if you like, the term "demonic infection." There really isn't a technical lexicon for this subject.
What would you call a person who has a demon (or demons) but is still high-functioning? Such people do exist. In fact, you probably even know some.
I have studied this topic for over 40 years and have interviewed people who have assisted in real exorcisms.
As you know, it is a very dangerous subject.
BTW, alcohol isn't called "spirits" for nuttin'.;-) See: A Spirited Debate: How Did Some Alcohols Come to Be Known as Spirits? (Scientific American)
In fact, a person might be possessed of a whole bunch of weak demons. We have to use metaphorical descriptions since we really don't have an intimate knowledge of that world.
Sometimes we don’t need demons: Satan has many people on autopilot.