The detector can slip up. It often confuses large organizational accounts like Barack Obama’s for bots, and sometimes stumbles on actual automated accounts like @netflix_bot, which any human would peg as machine-run. But that lack of human common sense is actually a strength, Davis said: Because the algorithm weighs hundreds of factors in determining botty behavior, it’s nearly impossible for bot-makers to game in the long run.

Running each candidate’s millions of followers through BotOrNot is technologically unfeasible, given Twitter’s data access limits. Instead, I drew a random sample from 270,000 retweets of the three main presidential contenders over Memorial Day weekend, testing about 11,000 with the detector.

The results: Using a 40-percent cutoff, BotOrNot indicated around a quarter of Trump and Clinton’s followers could be bots. But if the cutoff is bumped up to 60 percent—Davis recommends this, to reduce the possibility of @BarackObama-style false positives—Trump and Clinton’s bot counts drop to around 3 percent.

That is low . It may be evidence that most of Trump’s and Clinton’s retweets are generated by real people. But the bigger revelation concerns Sanders. Even though his Twitter account is almost as popular as Trump’s, with run-of-the-mill posts getting 1,000 retweets, it appears he has even fewer fake followers. Only 1.7 percent of all the people who retweeted him failed the bot test under the 60-point standard, half the rate of Trump and Clinton.

Sanders has both an enthusiastic fan base and a slightly lower profile than his two opponents, perhaps making him less likely to be spammed by unrelated marketing bots. But BotOrNot’s results also indicate his following might be ever so slightly more genuine than his opponents’—so when one of his tweets goes viral, one can be a bit more sure it isn’t some botnet ginning up interest.

The distinction between a bot and human isn’t always clear. Some accounts with high bot scores actually appear to be manned by a human and aided by automation, mixing original thoughts with rapid-fire retweets. Even users that are clearly bot-powered—75,000 favorites?—gave decidedly human responses when queried. The worst of these are a bit like a political campaign: just enough humanity to invoke empathy, but with all the efficiency and cost-effectiveness of a machine. But some are just real people doing their part to support their candidate, even if that means incessantly retweeting Trump’s O ’ Reilly appearances.

The bot-human hybrid is the future of election-year Twitter. The news feed, like ice-cream shops in battleground states, will be colonized by the modern political campaign for the digital equivalent of a photo op. But if BotOrNot is right, most of that is yet to come. For all its bot-hybrids, Twitter still appears relatively free from political manipulation, at least for the moment.