The Russians simply applied the techniques they'd already been using on their own citizens to the 2016 American presidential campaign, taking full advantage of the fact that no one would be able—at least until after the fact—to track their meddling due to the sheer inundation of postings targeted to specific pro-Trump voters. And America did not notice it was being “acted upon.” Our intelligence services were thoroughly, shockingly AWOL, possibly due to the fact that many of them were too busy reading Breitbart and the Drudge Report to begin with. In fact, if you believe Mark Zuckerberg, Facebook itself didn't notice it. Even though Russian-generated anti-Hillary, pro-Trump content is now known to have been shared over 340 million times.
But it was happening. Millions of Americans were viewing Russian-created ads for Donald Trump, engaging with Russian “bots” and provocateurs who claimed to be Trump supporters, and reading fake news stories, all actions geared to get them to hate Hillary Clinton with such a passion that they would crawl over glass to vote against her. And the traditional news organizations had no idea what was going on. In the meantime, the Trump campaign retained the data mining company Cambridge Analytica, which (it appears) acted as a vehicle to channel the Russian efforts to their targeted electorate.
And now we are looking at the result: President Donald Trump.
Source: How Facebook May Have Destroyed Our Democracy—For Good