British tweeters skew left and toward remaining in the European Union, which reflects their demographic makeup. “On average social media users are younger and better educated than non-users,” wrote the researchers Jonathan Mellon and Christopher Prosser in 2017. Users were also more likely to live in cities, “particularly wealthier areas with younger populations.” This phenomenon has been more thoroughly studied in the U.S., where The New York Times has reported that “the views of Democrats on social media often bear little resemblance to those of the wider Democratic electorate.” Active political tweeters in America were whiter, more left wing, more likely to be college educated, and less likely to say that “political correctness was a problem” than primary voters as a whole. Given the faux-democratic promise of social media, it is ironic that it has created a new establishment with roughly the same tight demographic boundaries as the old one.

Read: The dark psychology of social networks

How does this new establishment use its power? In Britain, political tweeters assail BBC producers and reporters with charges of bias. They make accusations that politicians cannot ignore, hobbling candidates by promoting sticky controversies on subjects that are low priorities among mainstream voters. They have more of an effect on the left than the right because of Twitter’s demographics. (Members of right-wing parties tend to be older.)

Of course, it’s not unusual for candidates to tack toward the extremes in membership contests, believing they can move back to the center when facing a national election. But the demands of the Twitter Primary risk saddling politicians with fringe positions they will struggle to moderate later. The stridency of highly polarized voices online also has a chilling effect on less engaged and less confident tweeters. The echo chamber of social media reassures those extreme voices that they are in fact the mainstream, even convincing Labour activists that the party was not set for a wipeout in the general election—before it received its worst result in almost a century.

Here’s one example of the Twitter Primary in action. In December, the Labour politician Rebecca Long-Bailey wrote an article that was seen as her pitch to be the party’s next leader. It was published in The Guardian, a newspaper that backed Corbyn’s Labour, and Long-Bailey herself is the anointed successor of Corbyn’s right-hand man, John McDonnell. The piece was mostly bland, but one phrase stood out: “progressive patriotism.” The top Twitter results for that phrase show the tenor of responses from the left. “We're now an electorate that can only be bought with racism,” reads one tweet with 1,400 likes. “Or ‘progressive patriotism’, to give it its latest fancy name.” (In the piece that officially launched her campaign, Long-Bailey did not repeat the phrase.) Yet to read so directly across from “patriotism” to “racism” is a fringe position. Some 67 percent of Britons describe themselves as “very” or “slightly” patriotic.” Telling two-thirds of the country that they are secretly racist is a courageous electoral strategy.