As FiveThirtyEight’s Ben Casselman noted shortly after:

What’s going on here? The Clinton campaign was clearly trying to show mutual ground between Americans and gun owners (their support for universal background checks). But Venn diagrams are supposed to demonstrate common areas of overlap by two separate groups. In this case, gun owners should be part of the Americans circle.

The Washington Post quickly worked up a new data visualization, and it did not involve circles. (While visualizing with circles is possible, reporter Philip Bump said “we didn’t feel like doing advanced math to calculate the size of the curved overlap.”)

Many others on Twitter, too, decided to use this as a teaching moment for Clinton, demonstrating how Venn diagrams work with Venn diagrams of their own:

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