From my new article in the ideas issue of Politico Magazine:

The calls for Donald Trump to release his tax returns began early during the campaign and never really let up. It was easy to assume he eventually would make good on his promises to turn them over. Every president since Jimmy Carter had released his taxes; Trump would have to do the same, right?

What we’ve learned since then, of course, is that Trump didn’t have to reveal anything. The Constitution doesn’t require disclosure; plenty of federal officials need to submit their tax returns to the Senate, but not the president. It’s just a norm.

One of the crucial lessons of the past year, turns out, is just how much of American politics is governed not by written law, but by norms like these.