CAN WE ALL SAY DISCOVERY.
The Supremes have ruled that sources are protected IIRC.
but, those records will not be.
GO FOR IT.
Assuming Cain brought a slander/defamation case (and I can't think of another cause of action that would be even remotely feasible), his case would probably not survive a motion to dismiss, so it would never even get to discovery. As a public figure, Cain would need to show that Politico acted with "actual malice," meaning that they knew that what they were publishing was false, or that they acted with reckless disregard of the truth. Considering that (a) Cain himself has confirmed a substantial portion of what they wrote (e.g., the existence of the settlement and the general subject matter of the complaint), and (b) Politico has been careful to couch much of what they've written in "sources report...." terms, it would be virtually impossible for Cain to meet this standard.
GO FOR IT.
I don't normally make predictions...at least not ones that can be tracked. :) Nothing will come of this. The Politico is in the clear.
Mark this post and gloat at me later...if I am wrong.