Cyrus laughs. Just, not in a way that implies that he thinks Stephen is joking.

"Of course you are," he says, blithe and friendly and reassuring. "Way too smart." Gullible enough to stockpile supplies for rebels on Reagan property, but way too smart to get recruited. "Besides-- why the hell would you want to go against the Capitol?" The answer is obvious in the question-- You wouldn't.

Telling Stephen what to think, telling him sidelong what's right and letting him believe the idea was his-- it's second nature. He's known for years that Stephen is stupid. That's exactly why he needs to be protected, isn't it? Why he's always needed to be protected. He's never wanted to be involved with anything bigger than his friends, his parties, shopping trips, his Sponsor meetings. Being involved in bigger things is Cyrus' job. This is the natural order of things, the way it works between them.

Cyrus has never for a second believed that Stephen is a traitor. That would require the brains to form a contrary opinion-- a skill that Cyrus has never credited his brother with.