2020 Democratic presidential candidate Sen. Bernie Sanders (I-Vt.) at a rally on March 16 in Henderson, Nev. (John Locher/AP)
Opinion writer

It is remarkable, really, that only two of the Democratic presidential candidates have disclosed their tax returns. Given how many are calling for President Trump to do the same and given the mess created by Trump’s refusal to release his taxes and to divest himself from his businesses, there shouldn’t be single candidate who doesn’t, well in advance of the first debate, release years of tax records.

That’s exactly what the Citizens for Responsibility and Ethics in Washington, the premiere good government group involved in an array of lawsuits and claims seeking to combat Trump’s opaqueness and conflicts of interest, is doing. In a news release Thursday, CREW put out a statement, asserting: “CREW is committed to not letting this president’s failure to disclose become the new normal. CREW Executive Director Noah Bookbinder recently testified before Congress supporting HR 1, democracy reform legislation that includes a requirement that presidents, vice presidents, and major candidates disclose their tax returns, and explaining what the public could learn from presidential tax returns.”

CREW will begin to keep track of Democratic contenders’ disclosures in the hopes of encouraging them to release 10 years of taxes:

Some 2020 presidential candidates have released nothing about their tax returns, while some have released 10+ years in full. Several candidates fall somewhere in between, and have shown specific members of the press certain years of returns, or summaries of their returns during past campaign cycles, including Cory Booker, John Delaney, Kamala Harris, John Hickenlooper, and Jay Inslee. When Bernie Sanders was running for president in 2016, he released only his 2014 tax return. These types of limited disclosures do not go far enough to shed light on possible conflicts, or to show the public a full picture of presidential candidates’ finances.

In fact only two — Sens. Elizabeth Warren (D-Mass.) and Kirsten Gillibrand (D-N.Y.) — have released 10 years of returns. The Democratic National Committee should have insisted that, in addition to its other criteria, the release of 10 years of returns be a requirement for participation in its debates. Likewise, all major Democratic groups (e.g., organized labor, environmental groups) should refuse to endorse a candidate who has not disclosed 10 years of returns.

Frankly, the failure to have done so by June when the first debates are held (especially Sanders, whose campaign extended through the entire 2016 primary cycle) suggests a candidate is not prepared to run for president, has suspicious finances, doesn’t really value transparency or all of the above.

However, it’s not enough for a candidate to release his or her returns. They should all agree to close down and/or entirely separate themselves from any nonprofit entity (as Sanders did when he closed his institute), release all financial information about those entities, reveal what monetary gifts they gave to universities to which their children applied, place all assets in a blind trust now, and agree that all Cabinet members and senior White House staff will do the same. While they are at it, they should pledge to employ no family members if elected, enforce a strict policy of commercial air travel for Cabinet members and lay out their own comprehensive ethics plan. (To date, only Warren has done so.)

It would be politically stupid for Democrats not to demand this of their candidates. One of the best arguments against Trump is his abject financial corruption and refusal to follow the norms of financial disclosure that every predecessor has followed. If their own candidate cannot show himself or herself to be purer than Caesar’s wife, how will they ever expect to hammer Trump for everything from nondisclosure of taxes to operation of business that he can promote from the White House and presiding over the most ethically challenged administration since the Richard M. Nixon presidency?

Read more:

Greg Sargent: The case for getting Trump’s tax returns just got stronger — and more urgent

Paul Waldman: We may finally see Trump’s tax returns, and Republicans are panicking

Harry Litman: To get Trump’s tax returns, Democrats just need to send a letter

Paul Waldman: The silly ways Republicans will defend keeping Trump’s tax returns secret

Jennifer Rubin: Are Democrats going to let Sanders get away with this?