Presenting the material which would have justified the assertion might have compromised HUMINT assets, technological capabilities, or both. There are sometimes valid reasons for not disclosing how you know what you know, and couching that information in more vague and intuitive terms rather than as absolute sourced information.
We’re not talking about disclosure of anything. We’re talking about simple defense of his claims. He wouldn’t even say “did to.” to those who said saddam didn’t have them. He wouldn’t help with anything.