In fact, the difference between the salary he reported to the tax authorities for 2005 (about $1 million) and what he earned that year appears to be as large as $3.5 million, and could be a good deal more.

Indeed, this pay gap could be the thorniest issue that arises for the president from Rachel Maddow’s big Trump tax scoop, which included the disclosure of two pages from Donald Trump’s 2005 tax return.

Trump has refused to release his full tax returns—breaking with a tradition for presidential candidates and presidents that goes back to Richard Nixon. But the publication on Tuesday night of a portion of Trump’s 2005 tax return is the second time in less that six months that details have emerged about what Trump may have actually paid, or not paid, to Uncle Sam over the years. In October, the New York Times published a number of key pages from Trump’s 1995 state tax returns.

Fortune was the first to report, last fall, that what Trump reported as “wages, salaries, tip, etc.” in 1995, a mere $6,108, was wildly different what other publicly available documents say Trump earned that year. In fact, Trump likely earned at least $4.8 million in salary that year.

For 2005, Trump reported to the IRS that he made $998,599 in salary, including wages and tips. That was again less than what other publicly available documents, and Trump’s own public statements, suggest that he earned that year. For instance, according to financial reports filed with the Securities and Exchange Commission, that same year Trump received $2.2 million in salary and other compensation from Trump Entertainment Resorts, the casino company Trump had taken public a decade earlier. The figure comes from a proxy statement that the company filed in early 2006.

Trump representatives could not be reach for comment. But in a statement responding to Tuesday’s release of Trump’s 2005 tax documents, a White House official said that Trump had a responsibility to “his company, his family and his employees” to pay no more tax than he was legally obligated.

And $2.2 million is not all Trump was likely paid by his casino company in 2005, a year in which he transitioned from being Trump Entertainment’s CEO to chairman. Under a service agreement, Trump was entitled to receive an additional $2 million annually from the casino company on top of his regular salary. Trump was also entitled under the service agreement to be reimbursed for his expenses related to the company.

Nonetheless, the 2006 proxy statement states Trump’s other compensation from the company as $1.3 million. So it’s not clear if Trump collected his full $2 million fee that year, or whether it was excluded from the company’s compensation table.

There’s more. The casino company in 2005 also paid Trump and his entities $337,000 for use of Trump’s airplane and golf-course to entertain the casino’s high rollers. The payment also went toward covering the lease on office space in Trump Tower in New York City.

In all, Trump’s casino company appears to have paid him and companies he controlled at least $2.5 million in 2005, and as much as $4.5 million. Not all of that would have been considered salary, but a big chuck of it would have been, thus pushing his true salary well about the reported $998,599.

And that’s just what Trump was paid by his casino company. Trump has publicly bragged that he made big bucks off his once popular business reality television show The Apprentice. By 2005, Trump was into his third and fourth seasons staring in the reality show. In an election financial disclosure form in 2015, Trump disclosed that he was paid $215 million over 14 seasons of The Apprentice, or an average of $15 million per season (though that number no doubt varied over the course of the program’s life).

Though the exact amount is unknown, Trump likely collected many millions from The Apprentice that year. It’s not clear where those payments show up on his tax filings. Trump did claim over $67 million in royalties, which include some of what he made off the show. But direct payments for appearing on television shows are normally recorded as wages, not other income.

Trump’s effort to report as little income as possible to the IRS was likely a perfectly legal way to lower his tax bill. And the tax documents revealed on Tuesday show that Trump likely paid more taxes that others have previously thought—$38 million in 2005 alone. But whether Trump paid as much taxes as he actually owed to the federal government is still a question that is up in the air.