1. The blue check mark spark

The earliest and most important dissemination of the video happened on Twitter, Mr. Decker noted. All it takes is a few widely followed, verified Twitter accounts to share a manipulated video to begin the rapid spread of disinformation. (Verified accounts, which are reserved for celebrities, journalists and other public figures, have a blue check mark next to their names.) In this case, a few writers from conservative outlets were the first to share the video.

With the imprimatur of the verified accounts, the video began to pick up traction on Twitter organically, as similarly minded conservative users shared it. According to VineSight, a company that tracks disinformation online, the vast majority of the engagement with the video on Twitter was organic — it was spread by real humans, not by bot networks and the like.

2. Moving off Twitter

Though it’s fast and loud, Twitter’s universe is finite. Disinformation can become even more dangerous when it moves to other platforms, particularly the darker corners of the internet. Within four hours of the initial tweet of the video, it was also posted on 4chan, Facebook and Reddit. On 4chan, the anonymous and unrestricted online message board, six separate threads promoted the video. On Reddit, eight threads were posted in the same amount of time.

Some of the posts on Reddit, however, were from the anti-Biden left — largely vocal supporters of Senator Bernie Sanders who were also sharing the video.

On Facebook, the video was shared primarily in closed groups, spreading in both far-left and far-right groups.