http://www.rab.com/public/political/2016PoliticalHandbook.pdf
The FEC’s federal campaign regulations extend to paid internet advertising. Political advertising on the internet must be accompanied by a disclaimer similar to disclaimers required in print advertisements.
The regulations affect commercial website advertising sold by broadcasters, regardless whether it is sold in conjunction with the sale of broadcast time. The regulations apply to all forms of website advertising, such as banner advertisements, streaming video, pop-up advertisements, and directed search results.
The handbook you linked to has to do with Internet versions of radio stations, a different animal than Twitter. There might be regulations about how campaign ads originating from the campaigns have to have a disclaimer. That eeven applies to signs. It has nothing to do with whether the Daily Mail, Pravda, Al-Jazeera or Drudge can refuse an ad from a campaign.