Usually, Venn diagrams are an effective tool to show where two or three things do and do not overlap. Mitt Romney's campaign chose to use a Venn diagram in a rather confusing way.
The diagram, which the campaign included in an email fundraising appeal sent out late Monday night, depicts President Barack Obama's "middle-class promise gap" on health care -- how he has failed to lower premiums for middle-class families, as he once said he would.
In the left circle is Obama's campaign promise to lower health care premiums by $2,500 for the typical family. In the right circle is the current state of those premiums: They've increased by $2,393 since Obama took office.
And the overlap -- usually reserved for what the two circles have in common -- is labeled the "gap": The Romney campaign says premiums cost $4,893 more than Obama promised they would (that's $2,393 plus $2,500).
It makes a political point, but not much visual sense.