Actually, the National Enquirer has been warned ... The McCain Camp is fighting back.
Why warn? Warnings are for the news cycle.
Just sue them. Deeds, not words.
However, in the case of McCain and Palin, there just may be good reason to sue the news organizations that are promoting these lies. They are clean, and the lies are pretty bad, and the organizations know they are lies or are reckless about the truth.