The two pages of Donald Trump’s 2005 tax return released by veteran tax journalist David Cay Johnston and MSNBC’s Rachel Maddow leave a lot of questions unanswered. But there are two things the document makes clear:

Trump was able to claim huge amounts of “negative income,” which substantially reduced his ordinary income tax burden. He paid $38 million in total federal income taxes on an income of $153 million only because of the alternative minimum tax, a tax provision Trump now wants to repeal as president.

Trump lists about $152.7 million in income for the year, most of it real estate income, business income, and capital gains, on the 1040 tax form. Less than $1 million of his income came in the form of ordinary wages. But under "other income" he lists $103.2 million in negative income — that is, money he lost in that year or past years on business ventures.

This negative income could take a few forms. It could be past business losses, carried forward. We know from the New York Times’s reporting that Trump claimed $916 million in losses in 1995, which he still could have been carrying forward in 2005. It could also be depreciation of assets his business purchased: Instead of letting companies deduct the full cost of investments like new buildings, the tax code requires them to “depreciate” the assets, or deduct their value over time.

Trump’s companies are “pass-throughs” that don’t pay corporate income tax and whose income is instead dispersed to shareholders, who are in turn taxed on it. So carrying forward business losses or depreciating assets would affect Trump’s personal returns.

If Trump were allowed to use all this negative income to offset his $152.7 million in income, his tax bill would've been a mere $5.3 million, for an effective tax rate of less than 3.5 percent. That's a really shockingly small tax bill, and a symptom of how investors with lots of pass-through income can face much lower tax bills than people with ordinary wage income.

However, Trump wasn’t allowed to claim all that negative income. That’s because of the alternative minimum tax, a provision that has existed in some form since 1969 and is meant to limit the use of deductions, exclusions, credits, and other provisions by wealthy taxpayers to reduce their tax burden. The AMT added $31.3 million to his total tax bill, bringing his overall effective tax rate to about 25 percent.

We don’t exactly know why the AMT hit him so hard. The White House said in a statement that the negative income was due to "large scale depreciation for construction.” The AMT has different depreciation rules than the regular income tax code, which in some cases can reduce the amount you can deduct.

Putting all that together, there’s still a lot we don’t know. But one thing is clear: Trump has proposed a tax plan that would have made his tax bill much, much lower.

Trump has a lot to gain from his own tax plan

Trump, like most Republicans, wants to eliminate the AMT altogether. The tax tends to hit rich, but not uber-rich, people hard (think families making around $400,000 a year), and that’s a constituency the GOP cultivates assiduously. But Trump is an unusual uber-rich person, with a huge AMT liability. This proposal would have given him, personally, $31.3 million in 2005 alone.

Just as crucially, Trump has proposed dramatically slashing taxes on pass-through income, even more than he wants to cut income taxes in general. Rather than subjecting this income to current income tax rates, or even the lower individual tax rates that Trump proposed, his first tax plan proposed to set the same rate that he’d have corporations pay: a mere 15 percent.

Given that the top personal tax bracket in 2005 was 35 percent, Trump’s plan would’ve halved his marginal tax rate that year and then some. People with income from wages, or capital gains, wouldn’t have gotten a break this large. It was reserved for people with companies structured like the Trump Corporation.

In mid-September, sources at the campaign suggested they were abandoning this plan. That made sense; the cut cost $1 trillion over 10 years, and served no obvious policy purpose other than personally enriching Donald Trump. But at the same time, the campaign was also telling a small-business group, the National Federation of Independent Business, that the pass-through cut was still a go, earning NFIB's endorsement in the process. When the New York Times's Binyamin Appelbaum reached out to the Trump campaign, they were vague but suggested that the pass-through cut was there to stay.

Trump isn’t alone on this plan, either. House Speaker Paul Ryan and House Ways and Means Chair Kevin Brady haven’t proposed a rate as low as 15 percent, but they have said they want a top rate of 25 percent on pass-through income, which also would’ve been a substantial tax cut for Trump in 2005. Their tax plan would also eliminate the AMT.

All of which is to say that the return unveiled on The Rachel Maddow Show suggests Republican tax reform efforts won’t just benefit Donald Trump the way they benefit all rich people. He would be helped an unusual amount, owing to the particulars of his tax situation, with his high AMT burden and large amount of pass-through income.