"...we have signed international treaties against torture, thereby becoming US law as per the Constitution..."

I'm no lawyer, but I thought we sign treaties and then we pass laws to enforce them. For example The Supreme Court is hearing a case right now on whether or not Texas can execute a Mexican citizen dispite the various treaties we've signed.

In any case I seriously doubt we've ever signed any treaty which stipulates people breaking it should be hanged by the state. Generally speaking punishment is left up to the country in question.

But you have a point, this is exactly the sort of thing that Congress could use to impeach Bush. Problem is lots of Americans don't view the torture of terrorists for the purpose of saving American lives as a crime.