George W. Bush and Dick Cheney are widely considered war criminals by many for starting the wars in Afghanistan and Iraq. There were many innocent civilians who died in both wars and this is where the war criminal part comes into play.
If we use this logic, Most American presidents become war criminals though. In fact. Most world leaders throughout history become war criminals. It's almost impossible to be a world leader and not be considered a war criminal by some. Especially if your country takes part in a war when you're the country's leader at the time.
Most modern leaders have not started wars of aggression. US presidents are unique in this regard, which is a consequence of the US being a hegemonic, imperial power following World War II.
