Rush Limbaugh wasn't the beginning though. For example, listening to Coast to Coast AM where they talk about alien stories and conspiracy theories which start off as a way to pass the time when you've got a 12 hour haul across the middle of nowhere and very few other options. Keep in mind, most of this started well before podcasts and Bluetooth so your options were extremely limited across vast sections of the country. I can see how a show like that could appeal to someone intellectually curious about things who initially just dismisses some of the wackier stuff. But that's just the beginning of the radicalization pipeline. No reasonable person just starts on Rush. They work their way up through softer, easier to swallow drugs first.

This is similar to how I view 4chan. I almost went down that path because I started viewing it as an edgy teen and thought it's just fun and memes, no one takes this stuff seriously. But over time it becomes normalized and they do start taking it seriously. Looking at it now and I assume as a "normal" person seeing it for the first time, it's crazy.