>>>The problem here is that Trump uses "fake news" to question facts, not opinion.
>>Not offhand, but a 5 minute search found this one.
>>https://www.factcheck.org/2019/12/another-dubious-trump-attack-on-fake-news/

OK. Which "fact" is Trump questioning there? The article seems to assert a "dubious Trump attack" because they can't find some low-viewpoint footage to exaggerate crowd size that Trump attributed to CNN.

The citation itself says "the CNN video shows the camera angle at street level, but also from above looking down at the crowd" followed by an image looking down at the small crowd (with a "dozens injured" chyron). I would prefer to see the "street level" footage for myself if I'm asked to believe Trump is lying about it. However, I can't find it - which, by the logic of this citation means that factcheck.org is mounting a "dubious attack".