This was licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License by OpenSecrets.org. I contacted them with a request that they release it under a Creative Commons Attribution-ShareAlike License, and their reply was:
"Dear Guy,
Thank you for your note. You have our permission to use the image you cite under the Creative Commons Attribution-Sharealike 3.0 Unported License.
Best wishes,
Sheila"
If anyone wants to see it, I can forward the email to them.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.