US Treasury Secretary Steven Mnuchin prepares to testify on "The President's FY2020 Budget Proposal"  before the House Ways and Means Committee on Capitol Hill in Washington, DC, on March 14, 2019. (Photo by Jim WATSON / AFP)        (Photo credit should read JIM WATSON/AFP/Getty Images)
JIM WATSON/AFP/Getty Images
US Treasury Secretary Steven Mnuchin prepares to testify on "The President's FY2020 Budget Proposal" before the House Ways and Means Committee on Capitol Hill in Washington, DC, on March 14, 2019. (Photo by Jim WATSON / AFP) (Photo credit should read JIM WATSON/AFP/Getty Images)
Now playing
01:40
Mnuchin denies request for Trump's tax returns
stacey abrams john kennedy split
POOL
stacey abrams john kennedy split
Now playing
07:39
'Ok, I get the idea': GOP senator cuts off Stacey Abrams on controversial voting law
CNN
Now playing
03:10
Weir on Biden's vow to cut emissions: It's incredibly hard
Now playing
03:05
Was QAnon used by foreign adversaries?
CNN
Now playing
01:28
Buttigieg: It's going to take a national effort to reach Biden's climate goal
Sen. Lisa Murkowski (R-AK) speaks to reporters as she arrives for the continuation of the Senate impeachment trial of President Donald Trump at the U.S. Capitol on January 29, 2020 in Washington, DC. The next phase of the trial, in which senators will be allowed to ask written questions, will extend into tomorrow. (Photo by Mario Tama/Getty Images)
Mario Tama/Getty Images
Sen. Lisa Murkowski (R-AK) speaks to reporters as she arrives for the continuation of the Senate impeachment trial of President Donald Trump at the U.S. Capitol on January 29, 2020 in Washington, DC. The next phase of the trial, in which senators will be allowed to ask written questions, will extend into tomorrow. (Photo by Mario Tama/Getty Images)
Now playing
04:08
Murkowski explains why she's voting for Biden nominee
President Joe Biden, accompanied by Vice President Kamala Harris, speaks Tuesday, April 20, 2021, at the White House in Washington, after former Minneapolis police Officer Derek Chauvin was convicted of murder and manslaughter in the death of George Floyd. (AP Photo/Evan Vucci)
Evan Vucci/AP
President Joe Biden, accompanied by Vice President Kamala Harris, speaks Tuesday, April 20, 2021, at the White House in Washington, after former Minneapolis police Officer Derek Chauvin was convicted of murder and manslaughter in the death of George Floyd. (AP Photo/Evan Vucci)
Now playing
03:01
'A step forward': Biden speaks after Chauvin's guilty verdict
CNN's Eli Honig explains how much time former police officer Derek Chauvin, 45, could face after he was convicted of second-degree unintentional murder, third-degree murder and second-degree manslaughter in the case of George Floyd.
CNN
CNN's Eli Honig explains how much time former police officer Derek Chauvin, 45, could face after he was convicted of second-degree unintentional murder, third-degree murder and second-degree manslaughter in the case of George Floyd.
Now playing
03:25
Here's the sentence Derek Chauvin could face after guilty verdict
CNN's Van Jones reacts to Attorney General Merrick Garland's announcement that the Justice Department has launched a federal civil probe into policing practices in Minneapolis following the death of George Floyd and the murder convictions for ex-cop Derek Chauvin.
CNN
CNN's Van Jones reacts to Attorney General Merrick Garland's announcement that the Justice Department has launched a federal civil probe into policing practices in Minneapolis following the death of George Floyd and the murder convictions for ex-cop Derek Chauvin.
Now playing
03:08
Van Jones reacts to Justice Department's Minneapolis police probe
CNN
Now playing
03:14
'Performative outrage': Avlon on GOP backlash to Rep. Waters
Two Honduran children found clinging to an island surrounded by a powerful current in the Rio Grande were rescued by Border Patrol agents and taken into custody, the region's top border official said, the latest example of the dangers migrants face as a growing number desperately attempt to reach the US.
U.S. Border Patrol
Two Honduran children found clinging to an island surrounded by a powerful current in the Rio Grande were rescued by Border Patrol agents and taken into custody, the region's top border official said, the latest example of the dangers migrants face as a growing number desperately attempt to reach the US.
Now playing
02:22
See Border Patrol rescue 2 migrant children in Rio Grande
Biden speaks from the Treaty Room in the White House on April 14, 2021 in Washington, DC.
Andrew Harnik/Pool/Getty Images
Biden speaks from the Treaty Room in the White House on April 14, 2021 in Washington, DC.
Now playing
02:59
Enten: Biden is focused on what Americans care about
CNN
Now playing
02:40
Biden says he's praying for 'right verdict' in Chauvin trial
ST. PAUL, MN - NOVEMBER 6:  Former U.S. Vice President Walter Mondale concedes the election to his Republican opponent Norm Coleman November 6, 2002 in St. Paul, Minnesota. Mondale and Coleman were in a race for U.S. Senate that was too close to call the evening before.  (Photo by Mark Erickson/Getty Images)
Mark Erickson/Getty Images
ST. PAUL, MN - NOVEMBER 6: Former U.S. Vice President Walter Mondale concedes the election to his Republican opponent Norm Coleman November 6, 2002 in St. Paul, Minnesota. Mondale and Coleman were in a race for U.S. Senate that was too close to call the evening before. (Photo by Mark Erickson/Getty Images)
Now playing
03:00
Walter Mondale dies at 93
george w bush congress immigration rhetoric cbs intv sot mxp vpx_00000000.png
george w bush congress immigration rhetoric cbs intv sot mxp vpx_00000000.png
Now playing
01:25
Bush calls on Congress to tone down 'harsh rhetoric' on immigration
WASHINGTON, DC - MARCH 23: Sen. Ted Cruz (R-TX) speaks at a Senate Judiciary Committee hearing on "Constitutional and Common Sense Steps to Reduce Gun Violence" on March 23, 2021 in Washington, DC.  Many senators spoke both for and against gun control the day after a shooting in Boulder, Colorado where a gunman opened fire at a grocery store, killing ten people. (Photo by Tasos Katopodis/Getty Images)
Tasos Katopodis/Getty Images
WASHINGTON, DC - MARCH 23: Sen. Ted Cruz (R-TX) speaks at a Senate Judiciary Committee hearing on "Constitutional and Common Sense Steps to Reduce Gun Violence" on March 23, 2021 in Washington, DC. Many senators spoke both for and against gun control the day after a shooting in Boulder, Colorado where a gunman opened fire at a grocery store, killing ten people. (Photo by Tasos Katopodis/Getty Images)
Now playing
03:18
Berman on Cruz's latest tweet: 'The pot calling the kettle violent'

For more on President Trump’s finances, watch CNN Special Report “The Trump Family Business” on Friday, May 17 at 9 p.m. ET.

(CNN) —  

On Monday night, as expected, Treasury Secretary Steve Mnuchin informed House Ways and Means Committee Chairman Richard Neal, D-Massachusetts, that he would not be handing over President Donald Trump’s tax returns.

That move will occasion a response from Neal – in the form of a subpoena, a contempt vote or a lawsuit. No matter what Neal chooses, this fight is headed into the legal arena sooner rather than later.

And it’s likely that it winds up, at some point, in front of the Supreme Court.

Which is, if you stop and think about it, remarkable. We are now using the Supreme Court to litigate something that, prior to Trump, was seen as de rigeur for people running for president. Sure, some candidates released more years of their tax returns. And some released less. Some did so with little prompting while others – Bernie Sanders in 2016 – had to be dragged kicking and screaming to transparency.

But, the point remains: Donald Trump was (and is) the only major party presidential nominee since Watergate to never release any past tax returns. He is also the only president to refuse to release even a year of past returns.

So, why? Why never release any tax returns during the course of the campaign? Why offer a variety of shifting explanations – under audit, too complex, no one cares – for why you aren’t releasing them? And why carry the fight possibly all the way to the nation’s highest court?

Mnuchin’s stated reason for not turning over the taxes to Neal is that the Massachusetts Democrat is not asking for the returns for legitimate reasons but rather to score political points – and, therefore, the Internal Revenue Service (and the Treasury) doesn’t need to comply with a little-known statute that allows a select few members of Congress to see Trump’s tax returns.

“In reliance on the advice of the Department of Justice, I have determined that the Committee’s request lacks a legitimate legislative purpose, and … the Department is therefore not authorized to disclose the requested returns and return information,” Mnuchin wrote to Neal on Monday.

No matter where you come down on that legal technicality, it still doesn’t explain Trump’s long-running resistance to releasing his tax returns. He’s been fighting against transparency on this front from the beginning of his candidacy – despite running a campaign in which he put his supposed wealth and success front and center.

Which gets me back to the question of why. Here are a few of the most likely reasons:

1) Trump’s not as rich as he says: There’s very little question that Trump overstates his personal wealth – and has done so for as long as he has had personal wealth. He’s said he’s worth $10 billion; Forbes said in 2018 that number is closer to $3 billion. For Trump to be exposed as one-third as rich as he had said he is would be embarrassing, sure. But remember, too, that Trump equates wealth directly with success and importance. So being exposed as less rich would be a blow to his success narrative as well.

2) He has Russia ties: While the Mueller report made clear that neither Trump nor anyone in his campaign orbit colluded with the Russians to help Trump win the 2016 election, it would still be a very big story if Trump’s tax returns showed he had extensive financial dealings and ties to Russia. We know, from Michael Cohen, that Trump and his family were deeply involved in the potential construction of Trump Tower Moscow and that Cohen lied about that involvement (and how long it stretched) to protect Trump. We also know that Donald Trump Jr. said this at a 2008 real estate conference: “In terms of high-end product influx into the US, Russians make up a pretty disproportionate cross-section of a lot of our assets. Say, in Dubai, and certainly with our project in SoHo, and anywhere in New York. We see a lot of money pouring in from Russia.”

3) He didn’t pay many (or any) taxes: We know – because Trump admitted as much – that he used a more than $900 million net operating loss for his business in 1995 to avoid paying personal income taxes for a number of subsequent years. How? This, from The New York Times, explains it:

“Known as net operating loss, it allows an array of deductions, business expenses, real estate depreciation, losses from the sale of business assets and even operating losses to flow from the balance sheets of those partnerships, limited liability companies and S corporations onto the personal tax returns of people like Mr. Trump. In turn, those losses can be used to cancel out an equivalent amount of taxable income.”

As the Times noted, Trump’s $916 million loss in 1995 could have allowed him to pay $0 in personal income taxes for the next 18 years.

4) He donates no (or very little) money to charity: We know, thanks to the amazing reporting of the Washington Post’s David Fahrenthold, that Trump long used his charitable organization to feather his own nest and collect political chits rather than for any philanthropic purposes. (Trump shut down the charity in 2018.) It’s not at all clear how generous (if at all) Trump has been to other charities over the past few decades. While there is no requirement for wealthy individuals to make large charitable donations, many do. And Trump has often boasted about the depth and breadth of his charitable giving.

Whatever the reason (or reasons), it’s very clear that Trump – soon after he became a candidate for president – reversed course on his past pledges to release his returns.

“I would certainly show tax returns if it was necessary,” Trump told conservative radio host Hugh Hewitt in February 2015, just months before formally entering the presidential race. A year later, after Mitt Romney publicly challenged Trump to release his taxes, the billionaire businessman’s approach had changed.

“You don’t learn anything from a tax return,” Trump said at a GOP debate in February 2016. “I will say this. Mitt Romney looked like a fool when he delayed and delayed and delayed and Harry Reid baited him and Mitt Romney didn’t file until a month and a half before the election and it cost him big league … As far as my return, I want to file it except for many years, I’ve been audited every year. Twelve years or something like that. Every year they audit me, audit me, audit me … I will absolutely give my return but I’m being audited now for two or three [years’ worth] now so I can’t.”

(Nota bene: There is no law that forbids a president – or any citizen – from releasing their taxes while under audit.)

What changed? Who knows! But, it’s quite clear that sometime between February 2015 and February 2016, Trump decided that whatever was in his returns would be far worse for him if it got out than the negative press he would take for not releasing them. And he’s not backing away from that decision. Not for anything.