They also touch on one of my personal sanity checks. Starfish Prime vastly increased the trapped electrons in the VARB. That's one nuke. Spread over a volume that's several times the whole Earth. We've set off, what, some five hundred nukes within the thin envelop of air of one Earth and the effects on the majority of humanity were negligible. That doesn't make the VARB particularly impressive.
(Yeah, I know...electrons, low energy electrons at that...but the idea is there.)