Zippy Catholic is burning up the blogosphere -- five posts in eleven days! (start here and work forward) -- on what he calls "legal positivism." (I say "what he calls" because others insist his use of "positivism" is idiosyncratic (or at least idio-something).)
In brief, the question is what a judge can or must do when deciding a case in which the relevent positive (i.e., man-made) law contradicts the natural law.
My one thought on this is in the form of a question: How well does the Catholic tradition on law mesh with the American system of checks and balances? For example, St. Thomas writes that "it belongs to the same authority to interpret and to make a law;" by this, he means the public authority in general. But what happens when the public authority that makes a law is as purposefully distinguished from the public authority that interprets the law as it is under the U.S. Constitution? Does everything still follow as St. Thomas wrote it, since all the branches of government are at least formally one public authority? Or must some adaptation of the Catholic tradition be done to apply it to the circumstances here?