Legislate Every Member of Congress and President to Have to Publically Disclose Tax Filings

BBC: IRS ordered to hand over Donald Trump tax returns to Congress

Although not required by law, every US president since 1976 - except Mr Trump - has released their tax returns.

Why is this not required by law? Shouldn’t the American public know what sort of business deals the chief executive has, specifically, with foreign economic entities? And how much tax they paid or, more importantly, didn’t pay?