The dispute between Bernie Sanders and Elizabeth Warren over whether he said a woman can't win may be the most explosive story of the Democratic primary so far — but it wasn't even the biggest story about Sanders on social media this week.The big picture: A viral video from right-wing Project Veritas about a Sanders field organizer underscores how splintered the partisan digital universe is — and how difficult it is to get different slices of the electorate to pay attention to the same things.It's a vivid lesson in what happens when a thriving conservative media ecosystem competes with the mainstream media.By the numbers: Of the 30 biggest stories about Sanders between Monday and Wednesday, seven were related to tensions between Sanders and Warren, resulting in 390k interactions on social media (likes, comments, shares), according to data from NewsWhip provided exclusively to Axios.Those were the days when the alleged comments were first reported, and when audio of the post-debate exchange was released.But 10 of the biggest stories were about the undercover video from Project Veritas, amounting to 426k interactions.Why it matters: The numbers highlight the divide between how much a story is covered in the media and how much of a groundswell is generated by readers online on stories that may not be visible to most of the country.What's going on: On Tuesday, Project Veritas released videos of an Iowa field organizer for Sanders making threatening comments. Conservative media picked up the video and it became the most-engaged story about Sanders during this period.The Daily Wire, Breitbart, the Washington Times and the Daily Caller were among the outlets that registered among the most-interacted stories.Between the lines: The 2020 primary has been fertile territory for right-wing publishers on social media that are looking to counterpunch against the wave of criticism against Trump in the last three years.Our 2020 attention tracker is based on data from NewsWhip exclusively provided to Axios as part of a project that will regularly update throughout the 2020 campaign.See all past editions of the tracker here.Data: NewsWhip; Chart: Chris Canipe/Axios - Note: Hover over the weekly rank on desktop to see articles and interactions for each candidate and issue.