<<I recall the lunatics on the left claiming that the Bush twins bad behavior was a direct result of bad parents.>>
That's funny, cuz I don't. Maybe you have some specific examples in mind?
For what it's worth, my own opinion is that when kids are in trouble with the law, there is ALWAYS some degree of parental responsibility, and the worse the trouble, the greater the degree of parental responsibility. This applies especially where the parents appear to be model citizens and model parents. We don't really know them in most cases and their public image is not the real indicator of their parenting. By their fruits shall ye know them.
I just want to make it clear, however, that I'm not talking about those tragic cases where mental illness intersects with the criminal law. Mental illness is a real tragedy and the parents can only do so much in the face of genetic predisposition.