"Trump's Twitter account saw an unusual spike in followers over the weekend, many of which appear to have been created artificially. [...] You can enter Trump's handle, @realDonaldTrump, into Twitter Audit, a service that assesses the authenticity of one's followers, and find that only 51 percent of Trump's are real."
Update: That link was from a year ago. I just did the Twitter Audit with the following result. Still, 10 million fake followers, at least some being bots and likely of Russian origin, can do a lot of damage.