The bizarre episode illustrates how easily misinformation spreads online, often with the help of the president himself. Right-wing websites that seek to support the president’s baseless claims, or simply attract clicks so they can sell more ads, often eschew the traditional principles of journalism, such as simple fact-checking. And the social media companies aid the cycle by making it simple to share misinformation, including via fake accounts, and by training their algorithms to promote material that attracts more attention, as sensational and divisive posts often do.