The Guardian: source for 35 page "dossier" is "consistently reliable, meticulous,

and well informed."

https://www.theguardian.com/us-news/2017/jan/10/fbi-chief-given-dossier-by-john-mccain-alleging-secret-trump-russia-contacts?CMP=share_btn_tw

Senator John McCain passed documents to the FBI director, James Comey, last month alleging secret contacts between the Trump campaign and Moscow and that Russian intelligence had personally compromising material on the president-elect himself.

The material, which has been seen by the Guardian, is a series of reports on Trump’s relationship with Moscow. They were drawn up by a former western counter-intelligence official, now working as a private consultant.

The Guardian has not been able to confirm the veracity of the documents’ contents, and the Trump team has consistently denied any hidden contacts with the Russian government.

SNIP

An official in the US administration who spoke to the Guardian described the source who wrote the intelligence report as consistently reliable, meticulous and well-informed, with a reputation for having extensive Russian contacts.

Some of the reports – which are dated from 20 June to 20 October last year – also proved to be prescient, predicting events that happened after they were sent.