The use of anonymous sources is vital for the effectiveness of the fourth estate. There are plenty of situations where telling the truth can get someone into a lot of trouble (see Edward Snowden, Chelsea Manning), even when it’s a truth that the general public has a right, or even a need, to know. The journalists and their editors make a judgment call on the trustworthiness of their source, and the reader needs to make a judgment on the sagacity of the journalists and editors in who they trust.
The Washington Post published a story citing anonymous sources who claimed that a secret CIA report concluded that actors linked to Russia affected the US election to help Donald Trump get elected. A lot of people dismissed this report out of hand simply because it was in the “mainstream media”, and they think that just because they misunderstood news stories in the past then the mainstream media lies.
There is a difference between “true” and “factual”. The Washington Post article is factual. It does not claim that Russia attempted to help Trump get elected, nor does it claim that the CIA thinks Russia attempted to help Trump get elected. It reports on claims by anonymous sources. The journalists and their editors obviously trust these sources, but how does the reader assess the trustworthiness of the source?
First, consider the Washington Post as a source. It relies on its reputation to conduct its business, as opposed to RT.com, for example, which relies on the patronage of the Russian government, or thefreethoughtproject.com, which seems to rely on clickbait headlines. If the Washington Post publishes too many stories based on anonymous sources that turn out to be false, their reputation — and therefore their business — is going to take a hit, so they’re very careful not to do that.
Second, consider what the anonymous sources are saying. Is it likely to be corroborated or refuted in the future? In this case we’re talking about a government agency, which is unlikely to let a completely false report of its findings stand. Further, this sort of story tends to get investigated, and indeed senior Republicans are calling for a bipartisan investigation into the matter, so the veracity is going to be checked. The Washington Post knew that would happen, and wouldn’t have gone ahead with the story unless they were certain of vindication.
The CIA could be mistaken, of course. This sort of intelligence is a notoriously slippery beast. However, we should assume they have a basic competency at their job. Could the CIA be outright lying? Again, it’s possible, but what would they gain? They’re likely to see their powers expanded under Trump, even more than they were with the previous few presidents.
Try to remember that you have to live with uncertainty, and rejecting or accepting something based solely on whether it fits the worldview you’ve concocted isn’t a valid way to interact with reality. If it makes you feel any better, even if something does contradict with your worldview it doesn’t mean your worldview is wrong.