What is the lesson in Saddam Hussein's decision-making for the prospect of deterring Iran?

In an article in the July/August 2012 issue of Foreign Affairs Amatzia Baram argues that while Saddam Hussein was technically rational in his reasoning, he was also "delusional and reckless" in his behavior.  As Baram puts it, the idea that "rational regimes can be counted on to act in predictable ways--turns out not to be true."  Among other points, Baram wants to warn that regimes pursuing delusional goals may behave rationally but prove very hard to deter.  Referring to Iran, Baram insists that rationality may be hard to read and that deterrence "is a more complex issue than generally assumed."  Yet, Baram reveals that top Iraqi regime figures were deterred from using chemical weapons precisely because they were convinced that the U.S. would respond with nuclear weapons (see p. 85).  
That sounds like a case for deterrence succeeding quite well, and that is the main take-away from the Baram piece, though not the one he imagines.

However opaque the Iranian decision-making process may be, is there any serious doubt that the Iranian leaders would fully expect a nuclear riposte if Iran should decide to use nuclear weapons against the U.S. or a U.S. ally?