Spend all your time on Twitter and Facebook and it seems that Twitter and Facebook must be essential to the far right’s appeal, and that a better social media ecosystem would suffice to deal with Trump or suppress Marine Le Pen or sideline Nigel Farage.

But if the other side is actually less online than you are, this assumption leads to two mistakes. First, you end up downgrading the obvious real-world forces driving populism’s appeal, persuading yourself that an algorithmic tweak or better fact-checking will deal with deep trends — economic stagnation, social crisis — that would exist with or without fake news.

Second, you lose sight of the ways in which your own information bubble is a potential radicalizing force — including for people observing it from outside, for whom it makes political liberalism seem like an airless world filled with hyper-educated ideologues. Indeed, on the evidence of a Democratic primary that seems made for the social-media bubble, it’s liberalism that’s being warped by online feedback loops and radicalization cascades.