Paying taxes forthrightly has long been a matter of civic pride for most American politicians, a demonstration of honesty and of a willingness to share in society’s burdens. Since the Watergate era, presidential candidates have released several years of tax returns, allowing voters to peer at their financial choices and discern their entanglements.

Mitt Romney has upended that tradition this year. He has released only one complete tax return, for 2010, along with an unfinished estimate of his 2011 taxes. What information he did release provides a fuzzy glimpse at a concerted effort to park much of his wealth in overseas tax shelters, suggesting a widespread pattern of tax avoidance unlike that of any previous candidate.

Mr. Romney has resisted all demands for more disclosure, leading to growing criticism from Democrats that he is trying to hide his fortune and his tax schemes from the public. Given the troubling suspicions about his finances, he needs to release many more returns and quickly open his books to full scrutiny.

The 2010 tax return showed that the blind trust held by his wife, Ann, included a $3 million Swiss bank account that had not been properly reported on previous financial disclosure statements. (The account was closed by the trust manager in 2010 who feared it might become embarrassing for the campaign. He was right.) It also showed that Mr. Romney had used a complex offshore tax shelter, known as a blocker corporation, to shield the investments in his I.R.A. from paying an obscure business tax.