Astroturf, something that Democrats always accuse Republicans, Conservatives, and any non-Democrat of using, is the practice of organizing people for protest activity.
It CAN be paid-for protesters, but can also include those not given money or other incentives, but willing to show up, hold signs, and shout slogans on command.
Why is this a problem?
Because, normally, only those who feel quite strongly about an issue or candidate will put themselves in a public arena. Someone that committed at least deserves a hearing.
That supposition that the individuals involved have 'a dog in that hunt' is up-ended when the person is found to be apathetic, but appearing due to the efforts of a few 'community organizers'.
One of those community organizers is Robert Creamer, who was caught on tape bragging about his efforts - which included the payment of up to $1500 a day.
You can buy a LOT of protest, including a willingness to commit violence and other crimes for a lot less than that.
What was even worse was that the paid protesters put on Trump shirts before getting violent, so it looked as though the Trump supporters were the criminals. At that time, they laid the groundwork for their current claims that Trump supporters are Fascists.
The Obama administration also laid down the framework for trouble for the next administration. There are 250 offices of Organizing for Action around the country. Hard to imagine that they will all decide to peacefully build playgrounds and tutor elementary students.