When is hentai illegal?

So I know that hentai is legal in the US, but to what extent? Does it include all types of it? Including loli and shota? From what I have read, it's legal since it is only considered to be a cartoon drawing. The thing is that I have heard, someone got arrested for possession of comics containing hentai, sentenced to 20 years I think?

So... legal or illegal? Or is it just going to be a grey area with loli and shota? I'm am very confused as to if hentai is fully legal or somewhat illegal? I'm not just talking about viewing it, but also drawing and sharing it (digital only).