This ciphertext was sent to a senator, attempting to blackmail him. Because it is a letter, it is likely to begin with the word "Dear."
WARNING: This cryptogram contains at least one "fixed point". These are letters of plaintext that encrypt to themselves as ciphertext. (For example, J encrypts as J, or something like that.)
A joint project of Brendan Bard, Prof. Gregory Bard, and Prof. Seth Dutter, University of Wisconsin---Stout (January 30th, 2019)