You mean like Wikileaks?
No, the 20% not 'believing' just the 'Anon. Official' - they are believing the information on the basis of verification by a journalistic institution with supposed credibility.
'Anonymous Sources' are a mainline source of journalistic information, and journos basically put their entire credibility on the line when they vet info and then communicate said information.
The press didn't lie when representing 'anonymous officials' in 2016 rather, they communicated the information. Where the press did a 'bad job' was misrepresenting the nature of Russian-Trump relations, which basically were nill.
The MSM seriously cast doubt on the legitimacy of Trump for a long time, frankly I think 'everyone actually believed it' and it was a surprise when it turns out Trump and his ragtag team were lying to the FBI for really no good reason at all and in fact had really no direct connections to Russia. Too clownish even to be actually corrupt, unless they actually were in some cases - as remember some major figures in Trump's campaign were eventually indicated. Trump's campaign manager, buddies, personal lawyer - all ended up in jail. That's not 'nothing'.
Ironically, if Trump & Co. acted responsibly during the Mueller investigation - his pleas of 'Unfair!' might have actually worked, but he's such a liar that he only makes himself look guilty.
But Trump's lies, in contrast to media spin, are a whole other level of falsity - he literally invents facts without any basis whatsoever.
He's not 'spinning' the facts, he's literally inventing them.
On election night when he said 'If they count the good votes, I win, the fake votes, they win' - this was probably the most dangerous statement he's ever made, he was verging on plunging the US into a garbage African Republic. At that moment it was clear that he had to go, he's a greater threat to the Republic than any foreign invader. He's willing to destroy democracy for his own power and vanity.
His world view is literally: "If I win it's because I'm great, if they win, it's because they cheated" irrespective of any reality.
Fox News, in the lat few days, has had to pull away from his statements quite a few times, it's shocking.