When Can You, and When Can't You?

I've been watching the tv this morning while cleaning the house before getting out of town, and there was Judge Posner on the tv, saying that he thinks the NSA domestic spying was legal. This raises the same question as his op-ed in the Post, which is, when can a judge give an opinion as to a question not before him . . . and when can't he? (Excuse the gendered language.)

I mean, next month we'll hear Judge Alito, Posner's peer, for now, answer again and again that he cannot answer questions about the legality of the NSA domestic spying because he needs to be impartial when the case comes before him, if it ever were to do so. But there's Posner, chatty cathy-ing his way across the news media. I guess Posner is just trying to ensure that he'll have to recuse himself, if and when?

Btw, one reason judges and judicial nominees shouldn't answer hypotheticals is that hypotheticals often lack key facts, and one doesn't want to lock oneself in before one knows all the facts. (This is probably not relevant when asked your opinion on the constitutional bona fides of Roe.) I think that Posner has committed himself to a position in this case too early. There's more news every day. How can he be so confident that he's right, that nothing that was done in this case was illegal/unconstitutional, when he doesn't know what was done . . . ?