They mean that leading members of the Bush administration are war criminals in the precise legal sense that they violated the imposing body of rules and regulations that have grown out of the post–World War II Nuremberg Trials and Geneva Conventions. These rules are known as "international law."
There's a reason I placed the term in quote marks — because I think it's inaccurate to describe these rules and regulations as laws. They are, strictly speaking, bilateral and multilateral treaties between and among governments.
Laws, by contrast, are written, enacted, and executed by governments, and they apply exclusively to those residing within territorially defined political communities (be they city-states, nations, or empires). Citizens of liberal democracies hold, moreover, that laws gain legitimacy — and become binding — only with the consent of the governed. And that standard is (tacitly) met only when the laws have been crafted by the people's democratically elected representatives.
"International law" fulfills none of these requirements.The Constitution of the United States:
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.The UN Convention Against Torture, passed by a two-thirds majority in the Senate and signed by President Reagan:
1. Each State Party shall take effective legislative, administrative, judicial or other measures to prevent acts of torture in any territory under its jurisdiction.
2. No exceptional circumstances whatsoever, whether a state of war or a threat of war, internal political instability or any other public emergency, may be invoked as a justification of torture.
3. An order from a superior officer or a public authority may not be invoked as a justification of torture.