American democracy has a target on its back: Disinformation has become a firm fixture of political campaigns in the digital age. Given the country’s polarized politics and history of close elections, the prospect that sophisticated influence operations, foreign and domestic, could shape the outcome of the 2020 presidential race is very real — and despite the searing experience of 2016, America is not ready.

A political crisis revolving around disinformation is easy to imagine. A group of voters could be targeted with falsehoods about when or how to cast a ballot. A doctored video could be released on the eve of the vote, depicting a candidate in a compromised situation or making a deeply offensive comment. Hackers could violate a candidate’s privacy to expose embarrassing personal information. If the 2020 election is tight, with the outcome hinging on just a few thousand votes, evidence of even modest interference could be destabilizing.

We learned from the Mueller report that the Russian government meddled in the 2016 election in a “sweeping and systematic fashion” through social media disinformation and documents aimed to sow divisions and disparage the Hillary Clinton campaign. We will probably never know whether those efforts changed the election outcome. By the time they were widely known, President Trump had been sworn into office. If a second presidential election shows similar signs of taint, our current crisis of faith will metastasize, undercutting not just the American political system but the credibility of democracy across the globe.

While many were blindsided by the impact of disinformation in 2016, next time around we’ll have no excuse. Researchers have documented advances in so-called deep fakes, fraudulent videos with such verisimilitude that they are virtually impossible to prove false. We now know that propagandists play off existing ideological divisions to sharpen discord, including by infiltrating bona fide interest groups and mobilizing real-world protests and activism. Private messenger apps and secret Facebook pages allow the microtargeting of manipulative messages so stealthy that no one but the intended recipients ever see them. Instagram is expected to be the next frontier in disinformation, with its highly visual, meme-based interactions beyond the reach of traditional detection tactics like fact-checking.