This is an update to the previous item, below.
According to Gizmodo, quoting former Facebook workers:
Facebook workers routinely suppressed news stories of interest to conservative readers from the social network’s influential “trending” news section, according to a former journalist who worked on the project. This individual says that workers prevented stories about the right-wing CPAC gathering, Mitt Romney, Rand Paul, and other conservative topics from appearing in the highly-influential section, even though they were organically trending among the site’s users.
Facebook workers routinely inserted stories into the “trending” news section that met their preferred political choices when such topics were not “trending”. Facebook routinely overrode their algorithm generated “trending” topics to manipulate readers into thinking a topic was trending when it was not in order to draw attention to specific stories and topics.
Facebook itself is operating an unprecedented, massive propaganda operation. Additionally, their own data shows that people are sharing less personal information and sharing far more externally produced content – literally, Facebook has become the idealized platform for propaganda operations.