Can Satan and the demons influence bad behavior in ways other that actually possessing a person?
Absolutely. Satan is portrayed as being responsible for all types of evil behavior—evil thoughts, words, and actions. Relatively few people are portrayed as being demon possessed, yet most people go astray in one way or another. For example, in the New Testament, Satan influences Judas to betray Jesus, yet there is no indication that Judas is actually demon possessed. Satan is the mastermind behind all evil activity and influences the human creature accordingly.