Presumptive Republican nominee Donald Trump said that he won't release his tax returns before the November elections because "there's nothing to learn from them."
But in the decades-long history of presidential tax returns, voters have learned plenty of interesting things from the public release of the records.
Here's a look at five interesting things in some recent presidential returns.
Mitt Romney had a lot of money in an IRA
When 2012 Republican nominee Mitt Romney released his tax returns, people discovered that he had between $20.7 million and $101.6 million tucked away in an IRA. The revelation puzzled even some private-equity experts, since the individual retirement account was capped by law at annual contributions of $30,000. "Assuming Romney was maxing out pre-tax contributions, as should anyone who can afford to do so, he still would have needed extraordinary returns within his tax-deferred accounts to build such a big balance," TIME's Dan Kadlec reported at the time. "He must have been investing in stocks and other high-growth potential vehicles, which produce a capital gain."
Barack Obama donated heavily to his controversial pastor
Then-Senator Barack Obama's tax returns in 2008 showed a huge spike in charitable giving during his presidential run, The New York Times reports, as his income rose dramatically from book royalties. Some of the largest donations went to the Trinity United Church of Christ, whose controversial pastor Jeremiah Wright posed problems for Obama on the campaign trail. "Wright had been Obama's pastor for nearly 20 years," TIME's James Carney and Amy Sullivan wrote at the time. "He had brought Obama into the church, helped him find his faith in God, officiated at Obama's wedding and baptized both his children. But Wright had also said a lot of incendiary things from his pulpit about America over the years, things that would be awkward to explain away for a politician hoping to unite the country and become the first African-American President of the United States." Obama's returns showed that he and his wife Michelle donated $27,500 to Wright's church in 2005 and 2006.
The Clintons' tax returns supported their narrative of the Whitewater land deal
When President and First Lady Bill and Hillary Clinton released years of tax returns in 1994, some documents supported the White House narrative about their Whitewater land deal that had been plaguing them with scandal. Earlier that year James McDougal, the Clintons' partner in the deal, suggested they had never invested more than $13,500 of their own money. "That sounded suspiciously like Whitewater was a sweetheart deal in which McDougal, who later headed a buccaneering S&L, made most of the payments in return for... just what, exactly?" TIME's Richard Lacayo wrote at the time. But the First Couple's tax returns from 1978 and 1979 show that they had actually invested enough money to claim about $22,000 in Whitewater-related deductions.
George H. W. Bush gave most of his income to charity
According to Mother Jones, President George H. W. Bush's 1991 tax returns show that he donated almost 62% of his $1.3 million income to charity in 1991. His gift recipients included the Yale Class of 1948 fund, the Desert Storm Foundation and the Barbara Bush Foundation for Family Literacy.
Richard Nixon took a huge amount of deductions
In 1970, President Richard Nixon and his wife made more than $200,000. They paid only $792.81 in federal income taxes. As TIME reported in 1973, "The deductions, if startling, were proper and permissible. ... The biggest deducation of $570,000 covered the gift of Nixon's vice-presidential papers to the National Archives."