ON SUNDAY, a senior aide to President Trump flatly asserted that the newly installed president is not going to release his tax returns because nobody cares about them. By the next morning, Kellyanne Conway had amended her story with a “#nonews” tweet that resurrected the flimsy excuse that it was an audit that was holding up release of Mr. Trump’s tax information. It was but the latest in a string of changing explanations and broken promises from Mr. Trump and his surrogates.

What has remained unchanged is Mr. Trump’s refusal to adhere to the long-standing tradition of presidential nominees and presidents releasing their financial information. By withholding information about his income, taxes and charitable giving, Mr. Trump fuels suspicions that he has something to hide and invites questions about what interests are being served by his presidency. That hurts both him and the country.

It was startling to hear Ms. Conway declare on ABC’s “This Week” that “the White House response is that he’s not going to release his tax returns.” She cited Mr. Trump’s victory in November and said, “People didn’t care.” That she felt the need to backpedal the next morning suggests she might realize that this is not the case. Hundreds of thousands of people have signed a WhiteHouse.gov petition calling for Mr. Trump to release his returns. A recent Post-ABC News poll showed that 74 percent of Americans, and 53 percent of Republicans, believe he should release the documents.

Indeed, Mr. Trump used to be one of those who believed that candidates for the country’s highest office had this obligation. Before deciding whether to run for president, Mr. Trump in 2014 said he would “absolutely” release his tax returns if he decided to run for office, something he had urged Republican candidate Mitt Romney to do in 2012. Once in the race, Mr. Trump promised there would be a release of the information “probably over the next few months,” attributing delay to the size of his returns, before latching on to what he said was an audit by the Internal Revenue Service. It has never been established that Mr. Trump is under audit, but if he is, tax experts have said that is not a bar to him voluntarily releasing the information. The fact that President Richard Nixon, not exactly a paragon of transparency, released his returns while under audit should embarrass Mr. Trump.

Release of Mr. Trump’s returns is especially critical given how complex — and unprecedented — his private business empire is. His tax returns hold the key to questions of whether there are potential conflicts of interest, particularly from foreign sources. Mr. Trump should end the delay in releasing his past tax returns and promise that when he files his returns for 2016, he will make them public without delay.