Even after he'd announced he would run for the presidency, he continued to dangle the carrot.
"I have very big returns, as you know, and I have everything all approved and very beautiful and we'll be working that over in the next period of time," he said in January 2016 on NBC's Meet The Press. "Absolutely."
At least half a decade and one Oval office term later, though, when it comes to his "big returns", Trump is playing a very different tune.
That switch in attitude happened, according to an analysis by CNN politics reporter and editor-at-large Chris Cillizza, within a month of Trump's Meet The Press interview, telling Anderson Cooper on February 24, 2016, that releasing the returns was "very complicated".
Within 24 hours, Trump had an excuse for not making them public: "I get audited. And obviously if I'm being audited, I'm not going to release a return," he said.
"As soon as the audit is done, I love it."
It wasn't getting audited or being too complicated, though, that changed his mind, Cillizza said, but the fact "that releasing his returns would be far more politically damaging than the negative publicity he would take for not releasing them".
Every US president since Watergate has released their tax returns, except for the 45th, who has spent the past four years doing everything in his power to ensure they never saw the light of day.
That legal battle came to an end on Monday, when the Supreme Court rejected the former leader's last-ditch effort to conceal his financial records from prosecutors. While the decision does not mean the documents will be made public, it does mean they can be shown to the grand jury in New York.
President Donald Trump pumps his fist as he tours a section of the US-Mexico border wall in 2021. Photo / AP
Trump swiftly retaliated, ranting in a statement that he is the victim of "the greatest political witch-hunt in the history of our country".
"This is something which has never happened to a president before," he wrote in the statement, adding that prosecutors "headhunting" him "is a threat to the very foundation of our liberty".
"In the meantime, murders and violent crime are up in New York City by record numbers, and nothing is done about it. Our elected officials don't care. All they focus on is the persecution of president Donald J Trump.
"I will fight on, just as I have, for the last five years (even before I was successfully elected), despite all of the election crimes that were committed against me. We will win!"
The "most likely" reason for Trump's reluctance, according to Cillizza, is that they would reveal two facts: That he didn't pay any taxes "for years and years" and that he has "massive debts".
According to a bombshell report by The New York Times last September, "Trump paid no federal income taxes in 11 of 18 years that The Times examined. In 2017, after he became president, his tax bill was only US$750 (NZ$1036)."
This could be achieved, Cillizza explained, "in large part by claiming more than US$900 million (NZ$1.2 billion) in losses on his 1995 tax return, which could have allowed him to avoid paying taxes for decades".
"Trump also aggressively sought to lower his taxable income, including claiming a US$72.9m (NZ$100.7m) tax refund that remains under investigation by the IRS," he added.
Also his "considerable debts – and the questions about whether or not he will be able to pay them – are likely the driving force for why Trump continues to work to keep his returns private," Cillizza said.
"If everyone knows he's in debt and with few options to get out of it, he loses any leverage he might have to go to the financial institutions he owes money to and renegotiate the terms of the loans."
Trump's "shifting stance on the release of his returns – and his ongoing battle to keep them private" are reflections on his always acting out of "self-interest" and being "purely transactional in all of his dealings", Cillizza said.
"Trump knows the details of the returns make him look bad and potentially kill any remaining leverage he has to dig himself out of the financial hole he is currently in," he added.
"And so, he fights like hell to keep them secret."
