Just before 9:30 p.m. on Sept. 13, the first Twitter post appeared, directing users to an obscure article about a remark Donald J. Trump had made last year that 50 percent of the country did not want to work.
Over the next 48 hours, 1,819 people, seemingly furious that the news media had paid more attention to Hillary Clinton’s assertion that half of Trump supporters fit into a “basket of deplorables,” lashed out at reporters and news outlets.
“Dear Media: If you don’t cover this, you’re covering for him,#Trump50percent,” wrote one Twitter user.
By the end of the week, the hashtag #Trump50percent had appeared in Twitter timelines more than 30,000 times.
Other liberal Twitter users, some of them with more than a million followers, linked to the article and spread the same complaint the Clinton campaign had made: that a shameful false equivalence was causing the media to soft-pedal Mr. Trump’s many transgressions and overplay the few it could find on Mrs. Clinton.
At first glance, the Clintonian grass roots seemed to have organically sprouted in anger. But closer inspection yielded traces of Miracle-Gro that led to the sixth floor of a building in the Flatiron neighborhood of Manhattan.
There, surrounded by start-up tech companies, “Star Wars” posters and flat-screen televisions fixed on cable news, Peter Daou sat with his team at a long wooden table last week, pushing the buttons that activate Mrs. Clinton’s outrage machine. Mr. Daou’s operation, called Shareblue, had published the article on Mr. Trump’s comment on its website and created the accompanying hashtag.
“They will put that pressure right on the media outlets in a very intense way,” Mr. Daou, the chief executive of Shareblue, said of the Twitter army he had galvanized. “By the thousands.”