The heavy research focus on the externalizing behavior cluster has been driven by an interest in identifying the core vulnerability trait, or risk phenotype, that precedes the antisocial behavior and substance abuse associated with adult SUD. To qualify as a candidate for the risk phenotype, the cluster would need to be relatively stable across time and contexts (i.e., it would have traitlike characteristics) and be mechanistically connected to the emergence of the adult characteristics. The externalizing cluster of behaviors in large measure satisfies these criteria. Its content involves both aggressive and delinquent behavior (Achenbach, Howell, Quay, & Connors, 1991; Krueger et al., 2002); the common element is difficulty in control of behavior, not affect. Aggressive behavior includes acts of verbal and physical aggression. Delinquent behavior includes conduct problems such as lying, cheating, stealing, and truancy; that is, it involves rule-breaking and acting in opposition to social norms rather than people. The correlation between the two behaviors in childhood and in adolescence is high (r ∼ 0.7), reflecting strong but far from perfect overlap (Achenbach & Rescorla, 2003). The externalizing construct
