Actually when a politician comes across this type of material, the correct action is to forward the information to law enforcement (at the federal level the proper agency is the FBI). The politician should not share the material with the press or other entities (friends, family, other politician, etc.) who are not law enforcement. McCain took the proper action here.
I would agree if McCain had not paid for its development. If he or an agent of his created it, he should completely vet it before he passes it around.
Which is why we need to know who paid for it and how they got it. its the difference between being a responsible citizen and perhaps criminal action... certainly libel and slander.
The paid-for part of the story is a detail added to the fake story to begin with...to give the original story some legs. Nobody on either side of the isle paid for this. It originated with a single anonymous joker who documented his trolling efforts on 4Chan. The troller's target was a single #nevertrump media pundit by the name of Rick Wilson, or at least Wilson is the dolt who hated Trump enough to bite on the bait. Wilson passed it to an ex-intelligence friend, who gave it to McCain, who gave it to the FBI. From there, apparently, the CIA also hated Trump enough to bite on the bile, and assess the "info" with some screwy level of high confidence.
Meanwhile Wilson and/or Buzzfeed is trying to get a number of news outlets to turn themselves into fake news outlets, and all but CNN and Buzzfeed turned it down.
It's unclear to me, and also to the president elect, whether the CNN/Buzzfeed source came from Wilson...or the CIA/IC. It's possible it came by way of CIA after Schumer suggested to Maddow that the IC has "six ways to Sunday" to exact revenge on any PEOTUS who disrespects thier pablum bulls.
More info:
http://www.zerohedge.com/news/2017-01-10/4chan-claims-have-fabricated-anti-trump-report-hoax
i read that mcain, some republicans and democrats paid their operative for the story.
that the operative may have gotten it from 4chan or somewhere else is irrelevant to assessing whether McCain acted responsibly or not. to me there is a big difference between having the dossier fall in your lap and paying investigators to create opposition research. If you paid for its development you are not a good citizen when you deliver libel or potential to the fbi.
now... my disclaimer is not of these sources are trusted by me. I could be analyzing fake news about fake news.