26 U.S. Code §6103. Confidentiality and disclosure of returns and return information

This is the statute which authorizes Congress (Chairmans of House Committee on Ways and Means, Senate Committee on Finance, or Joint Committee on Taxation) to request anyone's tax returns. This same law also authorizes POTUS or designed WH staffers to do the same thing.

IF Congress acquires and publicly releases Trump's tax returns, he can do the same to all of them.

(g) Disclosure to President and certain other persons

(1) In general Upon written request by the President, signed by him personally, the Secretary shall furnish to the President, or to such employee or employees of the White House Office as the President may designate by name in such request, a return or return information with respect to any taxpayer named in such request. Any such request shall state—

(A) the name and address of the taxpayer whose return or return information is to be disclosed,

(B) the kind of return or return information which is to be disclosed,

(C) the taxable period or periods covered by such return or return information, and

(D) the specific reason why the inspection or disclosure is requested.

https://www.law.cornell.edu/uscode/text/26/6103