In today's New York Times, I have an opinion piece entitled, "Don't Use the Ballot to Get Trump's Tax Returns." It begins:

Opponents of Donald Trump were outraged when, flouting recent tradition, he refused to disclose his tax returns during the 2016 presidential campaign. They remain outraged that he continues to decline to do so as president.

Now that political outrage is being channeled into legislation. Lawmakers in at least two dozen states have introduced bills that would compel presidential candidates to disclose their tax returns or be left off the ballot in 2020. The New Jersey Legislature recently passed such a bill, which sits on Gov. Chris Christie’s desk.

Mr. Christie should veto the bill, and other states should abandon their efforts. Making the disclosure of tax returns mandatory is bad policy and, in this form, probably unconstitutional.

Other recent pieces on this subject include those by Vik Amar and Rick Hasen. I approach this a bit differently--proponents, including Laurence Tribe, have styled this as a "ballot access" case, rather than additional qualifications (which, I think, are even more likely to be found unconstitutional), and I've addressed it from that perspective.