Hitchens' arguement is classic misdirection. The issue is that the USA did not have any credible evidence of its own on the Niger Yellow-cake issue and instead pointed to what someone else was saying about it - full well knowing that the credibility of that claim was discreditted as well. This is no different than the approach The National Enquirer uses to talk about aliens, Bill Clinton used when he redefined "sexual relations" to exclude fellatio or when he narrowly defined "is" to apply to only the relative present (and before you make the claim that WJC lied under oath - under Arkansas law - which was the applicable law, a deposition oath is only criminally binding if the case goes to trial, which it never did)
Given that the AUMF Section 3(a)1 requires Iraq to have been a continuing threat to the national security of the USA, this sort of lie is a violation of US law. But of course that won't be ever acted on.
So that leaves the original question - international law being used to indict Bush. And herein Bush, Cheney, Rice, Powell, Pace, Tenet, Gonzalez, Ashcroft and others are potentially in trouble. The Convention Against Torture Section 5(2) states
Each State Party shall likewise take such measures as may be necessary to establish its jurisdiction over such offences in cases where the alleged offender is present in any territory under its jurisdiction and it does not extradite him pursuant to article 8 to any of the States mentioned in paragraph I of this article.
Which in essence means that any signatory nation can indict a violator of the CAT, and if it doesn't and another signatory does and petitions for extradition, then that person has to be extradicted. This is what happened to Pinochet when he left Chile for medical treatment in London.
So that means that nations that are signatories to the CAT which has had citizens in Gitmo, may very well end up with a case filed agaisnt many in the GWB administration. And the governments may do this to get the US to honor the Alien Torts Act.
Now for GWB, who hadn't even been to Europe before becoming POTUS, this isn't going to be a big restriction. But for Rice, Powell, and many of the rest, it potentially cripples their future careers because they may very well be indicted for Crimes Against Humanity.