If someone doesn’t believe in demon possession, he/she can’t be a Christian. Its existence is clear in the Bible. To be a Christian you must believe ALL of the Bible — verbal and plenary. It’s not a Chinese menu to pick and choose what parts you want to believe.
I grew up with foreign missionaries frequently living in our home during their furloughs, and the stories they told left no doubt about demons and possession. In our dorm in Seminary, we had an issue that emanated from the Missions Professor’s office and an artifact he had brought from Africa.
And then there are Democrats.
“To be a Christian you must believe ALL of the Bible”
Well, not really.
I did not believe all the Bible when I put my trust in Jesus (I was a former Mormon, with lots of beliefs that were...off). Over the years, I have learned so much and saw how misled I was...but even though I was imperfect, Jesus still loved me, a sinner, and welcomed me as an adopted son.