It is possible for a professing Christian to become possessed with a demon.

        A church woman suffering from the power of the devil was asked how did the evil spirit get into her. The evil spirit answered back that she was at an adult motion picture watching a sex movie. This opened the way for the spirit to enter her. She was out of bounds of God's protection.

                When a person deliberately goes into devil's territory, it is possible to become a victim to whatever the devil offers, even claiming to be a Christian at the time.

Of course, she could not be possessed in her spirit but she was possessed in her body.