Some of them know it exists, but they themselves live in the democrat bubble. To them, Trump forums are just white supremacy sites and talk about... white supremacy things. And it's just sort of a vague boogie man like nebulous idea of what's outside the bubble.

Remember that these guys aren't just in the bubble, they are at the heart of the bubble. They not only don't see outside the bubble, they don't even see the people who are on the inner edge inside the bubble.

Many of them literally don't understand the rest of the world. Like literally, literally. They generally have the idea that the other side exists, but having never really seen or experienced it, and being older and set in their ways, they just don't even have an inkling of what it is.