Internalism and the Meditations

Here's a Cartesian idea: there is special epistemic access to facts about our own subjective, internal experiences. Other knowledge we may have, like knowledge of the external world, must be derived from the more basic knowledge, which concerns the internal.

This is clearly something Descartes thinks, but is there an argument to that effect? I'd always thought he did; the Meditations offers something like this:

1. There are possible skeptical scenarios for beliefs about the external world
2. There are no possible skeptical scenarios for beliefs about the internal
3. Being such that there's no possible skeptical scenario for it is the marker of the kind of epistemic fundamentality in question; so
4. The internal, not the external, is what has the kind of epistemic fundamentality in question

Premise (3) is no doubt dubitable, but I'll decline from dubiting it at present. I want to get clearer about (1) and (2). What's it take to be a skeptical scenario with respect to some belief? It seems like maybe Descartes treats a skeptical scenario with respect to a given belief as a possible case where one is wrong about that belief, but things seem exactly the same. But if that's the working understanding of a skeptical scenario, then it looks like we're just assuming the kind of internalism I'm looking for justification for. Why should we think the key question, for whether a given scenario has skeptical implications, is whether things seem the same? It seems that one would only sign up to that criterion if one were already convinced that seemings are really epistemically important.

Note that a more neutral characterization of skeptical scenarios might have it that a skeptical scenario with respect to p is a possible case where one is wrong about p, even though one has all the same basic evidence. But putting things this way, premises (1) and (2) become much less obvious.

So I'm tempted to think there's not actually any pressure in favour of internalism in Descartes's reflections on skeptical scenarios; reflection on which kind of deception is and isn't possible might just amount to teasing out the internalist commitments one initially finds oneself with.