I am very reluctantly coming to believe that there's about a 50% chance that a senior administration official will face a war crime trial either for ordering or condoning torture, or for the excessive bombing and civilian casualties in Iraq. I think it's most likely to happen after the official leaves office. It might be in absentia. It could be in Belgium, or in Germany, or (least likely) an international ad hoc tribunal. Already, SecDef Rumsfeld has had to cancel a trip to Germany to avoid the risk of prosecution.
Belgium recently changed its law to make it very difficult to launch war crimes prosecutions against foreign officials, and the supreme court there recently dismissed an attempted lawsuit against Bush. But meanwhile, a significant segment of Belgian public opinion appears to subscribe to the sentiment symbolized by this Wanted poster issued by a Belgian activist group:
Recall that the International Criminal Court agreement (.pdf) (to which the US is not a party) would prohibit these sorts of trials against our officials so long as we set our own house in order. But we are not doing that.
I wonder how long it will take the new Iraqi government to join the ICC? Joining would give the ICC jurisdiction over all actions on Iraqi soil dating after the accession. Regardless of whether they were committed by Iraqis. Then again, joining the ICC without agreeing to exclude jurisdiction against US forces would run Iraq into retaliation from the US: the US has halted military assistance to several nations that have refused to sign 'Article 98 agreements' by which they promise not to surrender US nationals to the ICC.
Update: If I had to bet right now, I'd bet it's the wanton harm to civilians (which I suspect is vastly underreported in the US) that would be most likely to trigger a trial, not the prisoner abuse. But should these allegations of systematic rape in captivity, coupled with claims that the Pentagon is stonewalling by trying to avoid inquiries prove to be true, that might alter the odds.
PS. As noted in the comments, my intent in this particular post was to be positive, not normative. Under what circumstances if any a foreign war crimes trial of a former US President or Cabinet official could ever be be a good thing is very hard for me to think coherently about, as I so passionately want the US to act in a way that makes the whole question absurd.