IMHO, the real reason that Bush is shutting up about WMD evidence is to save Putin's government. Bush figures taking the domestic political heat is less troublesome than dealing with the kind of (heavily nuclear armed) fascist dictatorship that might follow Putin's demise in Russia.
It may be that Bush won't be able to squash discussion of WMD evidence. If Democrats think he's 'lying or hiding' something, they'll find a way to use it. Domestic political heat over illegal immigrants, broken borders, and fighting a PC war in Iraq with two Marines butchered and others charged with murder. None of this is pretty. Bush isn't running again, but you'd think he'd have a care for republicans who are.