Not a lawyer so I'm reproducing some of the news that I read. What I think is that US did not loose the ability but the will to prosecute and is letting all run free...
Some differences in Brazil:
1. In Brazil free speech right is not above other rights. So you cannot disguise your hate vitriol as "free speech"
2. This is a bit of controversy - Brazilian judiciary opened an investigations on fake news without being provoked by the Attorney general office (procuradoria geral)