A tax return is far from a complete picture of a person’s financial life. For one thing, it is an accounting of income rather than wealth, so it would not establish whether Mr. Trump is a billionaire. But Mr. Trump’s tax returns could provide significant information about matters of greater public import, including his debts a nd the sources of his income. For example, if Mr. Trump deducted the interest payments on a loan from his taxable income, he would be required to disclose information about the source and amount of that loan. Another example: A partnership that sells real estate, and includes foreign partners, must disclose information about those partners.

If Mr. Trump holds money in foreign tax havens, those investments would be listed, too.

The disclosure of Mr. Trump’s tax returns could also help to verify, or falsify, a range of assertions that Mr. Trump has made about his own life — stories that he used to build support for his candidacy and continues to use to build support for his policies.

One straightforward fact-check: Mr. Trump repeatedly said he would not benefit from the tax cuts passed by Congress in 2017. He said that he would be a “big loser” and that the plan “is going to cost me a fortune.” The claim is absurd on its face. Virtually every major analysis of the tax cut has shown that wealthy people like Mr. Trump are the primary beneficiaries. But despite Mr. Trump’s best efforts, facts remain stubborn things with special power, and the release of his tax returns would allow a precise calculation of just how much money the president put into his own pocket.

R eporting on Mr. Trump’s financial past by Times reporters, including David Barstow, Susanne Craig and Russ Buettner has already undermined the president’s confected image as a hugely successful businessman. In a piece published Tuesday evening, Ms. Craig and Mr. Buettner reported Mr. Trump “appears to have lost more money than nearly any other individual American taxpayer” year after year in the late 1980s and the early 1990s. Mr. Trump has long said he suffered setbacks during the recession in the early 1990s, and then bounced back to rebuild his fortunes. But tax records and other sources show Mr. Trump lost big during the boom years of the late 1980s.

Far less is known about Mr. Trump’s more recent financial dealings. His federal disclosures provide estimates of revenue rather than profits: In 2017, for example, Mr. Trump reported that his Irish golf business had revenues of $14 million, while a separate report to Irish regulators said the business lost about $2 million. For most of Mr. Trump’s ventures, there is no public account of the bottom line.