The letterhead "Office of the Secretary" shows that it is definitely not the Secretary but rather someone on the Secretary's personal staff. Also it would not be the Deputy Secretary since that person would have their own Deputy Secretary letterhead. There is a good clue in towards the end where the writer refers to themselves as an assistant to the Secretary. A Secretary will typically have a number of personal assistants who the Secretary brings in under the White House political appointee process. These kinds of appointees are typically personal friends of the Secretary and who have shown unswerving personal loyalty to the Secretary. Also, the White House political appointee process means that they do not have to go through Senate approval like a Secretary would. And these kinds of political appointees do not have to have any particular qualifications like career employees must have. And they can be appointed with a very high salary without having to show they warrant a high salary like career people must do. I've worked with many of these kinds of appointees over the years as their bosses are hard to get face time with. The worst case I ever had to work with was a 21 year old who had just graduated with her Bachelor's degree and had never had a real job before her appointment as a special assistant. And she was appointed at the highest rank and salary in the Federal government. Of course she had to leave when the Secretary she was serving left. Or later with a different Secretary, I had to work with two women who were appointed where one was made the Secretary's Chief of Staff and the other her personal assistant. Neither had any qualifications for the work of the Department other then having been the Secretary's college room mates.