Breaking down the numbers. Here's his conclusion, which makes sense to me:
Drum has made clear that his purpose in doing this article was to get further research and attention on the topic. He has succeeded, and I think it a worthy goal. Before reading his article, I had the intuition that lead exposure should have some effect on crime. Reading the article strengthened this belief. I think it should strengthen this belief in any rational person who has not previously seen this evidence. But that is way short of making a convincing case for spending $400 billion of taxpayer money.