CNN reports that both Obama and Trump had been given a two-page briefing in early January that summarises the dossier.
Buzz Feed then reports on, and publishes in full, the dossier itself.
Trump has dismissed the reporting on the dossier as "fake news." Here is a brief timeline showing when, and how, it surfaced: A person whom the website Mother Jones identified as a "former senior intelligence officer for a Western country who specialized in Russian counterintelligence" begins researching Trump's links with Russia for "an opposition research project originally financed by a Republican client critical of the celebrity mogul," according to an article published in October by Mother Jones' Washington bureau chief, David Corn: "In June, the former Western intelligence officer — who spent almost two decades on Russian intelligence matters and who now works with a US firm that gathers information on Russia for corporate clients — was assigned the task of researching Trump's dealings in Russia and elsewhere, according to the former spy and his associates in this American firm.
This was for an opposition research project originally financed by a Republican client critical of the celebrity mogul.
The document contains allegations that Trump declined various business deals in Russia but that the Russian government fed Trump intel throughout the election. John Mc Cain knew about the dossier over a month ago.