Anyone who watches how the Western media and political class construct their ‘truths’ will have noticed the rough elements of the pattern. Something can be suggested in one quarter, for example in the US State Department, and then some ‘evidence’ is adduced – circumstantial, based on probability and relying on the most curious of sources (for example ex MI5 officers freelancing for a bit of extra money) but evidence nonetheless. At this stage people talk about “high probability”. But, wait a few weeks and what was previously a question of probability is now assumed fact. And the truth has also been cleansed of its dubious sources. It is simply cited as as obviously true as the earth is round and therefore there is no longer any need to reference it. And, it seems that 90% of them believe it themselves.
It turns out that this is an age old practice. Russian (Ukrainian) writer Nikolay Gogol had seen it all in the 19th century:
That both ladies were finally and unshakably convinced of that which they previously had been supposing as mere supposition is nothing unusual. Our fraternity, we intelligent people, as we call ourselves, behave in almost the same way, and our learned discourses serve as proof of that. At first, the scholar approaches them like an uncommon kind of blackguard. He begins timidly, moderately, he begins with the humblest kind of inquiry: ‘Is that not the origin? Was it not from that particular little corner that such-and-such a country received its name?’ or, ‘Does this document not belong to another, later time?’ or, ‘When we say this particular people, do we really not mean this other people?’ He immediately cites this and that ancient writer, and as soon as he detects a hint or something that strikes him as a hint, then he hits his full stride, plucks up his courage, feels perfectly at ease in conversing with the ancient writers, puts questions to them and even answers them himself, completely forgetting that he has started out with a modest supposition. It now seems to him that he sees what’s what, that it is clear, and his discourse concludes with the words: ‘And so, this is how it was, this is how a certain people should be understood, this is the viewpoint from which we should look at the topic!’ Then, from the lecture platform, he declaims it for all to hear, and a newly discovered truth embarks on its journey through the world, gathering to itself followers and admirers. 
- Gogol, Nikolay. Dead Souls (Penguin Classics) (pp. 212-213). Penguin Books Ltd. Kindle Edition.