Actually I wasn't really interested, but what with Trump and his well-paid lawyer team coming up with various, some conflicting, reasons, I must say I get a bit curious.

The hype on "personal", "constitution" and so, simply means that even the very small number of people who have the right and authority to ask as being snubbed, sidelined. Interesting is that when Trump c.s. talk about political crusade they seem more fearful of possibly having parts leaked than being secure in the knowledge it would have been the select few (with at least one democrat, U.S. House of Representatives tax committee Chairman Richard Neal who asked for the returns) who could be blamed. The political coin out of that doesn't seem to weight up to the risk of 'the people' knowing more than Trump wants.

"White House to Democrats seeking Trump tax returns: 'Never'"
finance.yahoo.com/news/white-house-resists-release-trumps-tax-returns-140939723.html

"Battle begins over Trump tax returns"
thehill.com/homenews/sunday-talk-shows/437746-battle-begins-over-trump-tax-returns