It would be the same thing exactly, except the analogy breaks down because Trump was a presidential candidate and is now president. Candidates for high office typically and traditionally release their tax returns for public view. Now that we have a president who chooses not to do so, the tradition has become an item of public debate and some lawmakers at different levels are proposing legislation to make tax return disclosure a condition of having one's name listed on the ballot.
You seem to be advocating for the "because I want it really, really badly, I should therefore have it," argument. It doesn't break down simply because someone was a candidate and is now the president. There is no question that the private lives of candidates and elected officials (and their families) will more or less become public record, one way or the other.
We all well remember how the public salivated over news of stained dresses and misused cigars; signs of Hillary Clinton's excessive coolness cracking under scrutiny; and how much the President lied and dissembled when faced with uncomfortable questions about his private life. His detractors pointed to the fact he lied to Congress as a sign he was unfit for leadership of "the free world", while his supporters maintained that what went on in his private life, outside of his policies and activities in the capacity of President, are irrelevant to whether he's a good President. All in all it was unseemly and creepy in the way the public ate it up.
The general public, and the news media as the public's proxy, certainly behaves as though it has a right to pry into all the nooks and crannies of government officials' private lives. It may be a result, for some people, of a genuine desire to accurately evaluate the character of people who accept positions of responsibility for the security and prosperity of the nation. For others, it may be a result of partisan bickering and looking for any material that can be used to make an
ad hominem argument against a particular candidate for office. Maybe it's all really just a result of a prurient desire to learn the sordid details of others' lives, treating them more as objects of entertainment in the spirit of soap operas than as human beings. But in any case, when it comes to the legislation of prying into the nooks and crannies, if it is viewed as the result of partisan bickering, the Supreme Court has always taken a very dim view of it.
Candidates and public office holders are already required to disclose a good deal of their personal financial information. Legally, it is a small step from that to mandated tax return disclosure. Under current law, public officials do not have the same privacy rights private citizens do. Expanding that to include tax returns is not a big legal step.
Legally, it's actually quite a large step from the current Ethics in Government Act, which requires an astounding amount of privacy disclosure, to tacking on the requirement to make public one's tax returns. The Ethics in Government Act has never been challenged in court, and it's on tenuous legal ground as it is. Both majority and dissenting SCOTUS opinions in cases that dance around the Ethics Act strongly indicate that if it were to ever be brought before the court that it would be struck down by a near-unanimous ruling.
In one case that dealt directly with a portion of the Act (Title VI, the Office of Independent Counsel),
Morrison v. Olson, it was ruled by the Supreme Court as being constitutional, in a 7-1 ruling. Justice Scalia's lone dissenting opinion was a scathing one, and predicted what would happen over the next few years that would result in Congress letting the Independent Counsel Act expire and rewrite that section giving back the authority of enforcing laws to the Executive branch of government. He correctly predicted that such a usurping of power would be abused in a partisan manner, as it was when the Special Prosecutor indicted Caspar Winebeinberger on charges related to the Iran-Contra affair, and with Kenneth Star and his gazillion dollar investigation of Bill Clinton.
None of that case really had anything to do with the financial disclosure sections of the Act, so the Justices didn't rule on that part. They did, however, have plenty to say about it, though. In the majority opinion, they questioned the constitutionality of the level of the financial disclosure requirement, calling it "excessive levels of disclosure," and a "gross violation of privacy." The opinion also noted (and spot-on predicted) that the Act would repel good people from serving in the government, the Executive branch in particular, because of the excessive levels of disclosure, the difficulty people would have divorcing themselves from their business interest, and in how the act limits income for those in office and favors those with "unearned" wealth over those with "earned" wealth.
To just up and expand the Ethics in Government Act to encompass federal tax return disclosures is a big leap legally, and would almost certainly see it challenged in court, and would almost certainly see the entire Act ruled unconstitutional by the SCOTUS.
The Ethics on Government Act was passed on the heels of the Nixon resignation, the Saturday Night Massacre, other assorted and sundry national scandals, and Congress voting itself a big, fat raise. They passed the Act as a means to placate an angry populace, and it was bad legislation that even those who voted for it at the time admitted.
Politically, it is a different matter. But if the large electoral vote states of New York and/or California pass laws that mandate presidential candidate tax return disclosure, it's a done deal.
Well, it's a done deal until it gets to the Supreme Court, where the States would have to convince the Court that such a legal mandate does not add any additional requirements to those found in the Constitution for the Office of the President, that any such ballot requirement is in the national interest, and that it is not as result of partisan politics. Historically, state ballot measures that have failed to meet any of those three requirements have been struck down by the Court. Even if the Court were to allow such a ballot measure, they would almost certainly restrict it from applying to any sitting President and Vice President.
