In the 2016 Presidential Election Donald Trump became the first candidate for 40 years not to release his tax returns.
During a Republican primary debate in February 2016, Mr Trump said that he wanted to release his returns but he stated an audit was being conducted on his financial affairs by the IRS; however there are no actual legal barriers not to show them. In September 2016 Trump's political partner, Gov. Mike Pence, dutifully released ten years of his family's tax returns, indeed as have all previous candidates from both major political parties have done since 1974.
The reasons for releasing them are simple: to show transparency, fairness, trust, integrity and the willingness to contribute to society - traits that we all deserve to see from our President.