He finally realizes that he was once president of the United States. He calls it "a very valuable lesson." I think the lesson he really learned is that his sleazy tactics didn't actually work. When dealing with sociopaths like Bill Clinton, it's important not to fall into the trap of thinking they are capable of moral self-evaluation. But they are capable of rational self-interest. If it becomes the Clintons' self-interest to smear other Democrats in future, they will not hesitate for a second to do so.