The crime reduction reliably occurs 20 (23, from the graph?) years after the lead reduction; there's no response in the crime rate until the less-lead-exposed babies have become adults.
The politicians who tackled crime (or didn't, or did whatever) 20 years ago haven't been in power most of the time since then, generally.
I've read about this theory before; it's impressive and (to me, at least) pretty persuasive.
To paraphrase a comment I made further up, banning lead in gasoline is a binary initiative that doesn't take a long time to initiate. Cracking down on crime is a longer process.
The politicians who tackled crime (or didn't, or did whatever) 20 years ago haven't been in power most of the time since then, generally.
I've read about this theory before; it's impressive and (to me, at least) pretty persuasive.