The question was: Can a Christian be possessed by demons?
The answer is NO. The devil may have jurisdiction on earth in it's fallen state. But The Holy Spirit lives within all believers. Think of it this way, God is the Sheriff and believers are his deputies. We as believers have authority over demons. They fear us and scurry away when we are near. But the believer must know who he/she is through Jesus Christ. Believers can cast out demons with the name of Jesus Christ. Some demons are more powerful and will require prayer.