Does Holder Really Have A Choice?

I don't see how proof that government officials waterboarded a prisoner 183 times leaves the attorney general any discretion at all. Here's the United Nations' Special Rapporteur on torture, Manfred Nowak, explaining the treaty that Ronald Reagan signed and championed:

If under the direct jurisdiction of the United States of America, a government official - whether it's a high official or a low official or a police officer or military officer, doesn't matter - whoever practices torture shall be brought before an independent criminal court and be held accountable. That is, the torturer, him or herself, but also those who are ordering torture practices, or in any other way participating in the practice of torture. This is a general obligation, and it applies to everybody; there are no exceptions in the Convention...

If you define torture in the way as the United Nations Convention actually is requiring, it's clear that many of those methods including waterboarding etc. fall under the definition of torture and persons can be prosecuted under the US Code. In addition, of course, you have other provisions -- you have the Fifth and Eighth Amendments to the US federal constitution - I mean , the legal possibilities for bringing perpetrators of torture to justice under domestic United States law exists. It's just a question whether they are applied or not.

So when does the U.S. formally withdraw from the UN Convention on Torture? And why isn't the pro-torture right advocating that?