The "for purely political reasons" is your own partisan spin on it.
What you're suggesting as a principle is that it's OK for the WH to have access to any return it wants - it does, obviously, given the IRS is under the WH but also in Sec. 6103(g) per the link below - but that the Congress, with the power to tax and spend, and oversight duties, must ask permission from the WH to see tax returns as a group, or the tax return of a person or entity. It's not defensible as a principle that I can identify.
The law is also crystal clear.
26 U.S. Code SS 6103 - Confidentiality and disclosure of returns and return information | U.S. Code | US Law | LII / Legal Information Institute
Read the bolded. That's been the law since 1924.
Those interested can read more about the purpose of the law, why Congress gave itself the same access the President has, and more, here:
How to Get Trump’s Tax Returns—Without a Subpoena - POLITICO Magazine
https://www.washingtonpost.com/opin...0e57e57e05d_story.html?utm_term=.633f578cfa99
Both articles are by George Yin, a UVa law professor and expert on the subject. There's nowhere in the law that says Congress must even state a reason, and certainly nothing in there says the Secretary gets to make the call whether the stated intent is sufficient reason.
You've done taxes for a while - what part of that law appears optional to you? In my experience dealing with the IRC, "shall" means
shall, and "any" means
any.