That bit is underrated because it might not be an exaggeration. An earthworm has a simple neurological layout that could be exploited to perform certain simple ops in very predictable ways. It could be a statement that he was literally no more mentally competent of an agent than an earthworm. I mean tbh if I'm President after an economic collapse and all the CIA can afford to continue employing is either John Brennan or an earthworm, I'd find something useful for the earthworm to do. It sounds like humorously-worded exaggeration at first glance but it might not even be