OK let me start off by providing a base of knowledge in US taxation.

Trump is an individual and he pays taxes individually by filing a 1040.

he also owns business interests which have been detailed in part via this wapo article: https://www.washingtonpost.com/politics/2019/05/21/trumps-complex-web-business-interests-visualized/
These other entities may file a tax return or they may not.

Let's look at an LLC for example.

Any LLC owned by one member (owner) reports its income on a Sch C.
An LLC owned by 2 members reports its income on a 1065 (partnership return) and issues a K-1
Generally partnerships dont pay US tax on income, that income is allocated by ownership % and reported via the K-1. The partner then reports this income on his/her 1040.

More members of the LLC just mean more K-1's.
Continuing with LLC's -

An LLC can ELECT S-Corp status wherein it files a form and when accepted files an 1120S (S-Corp return)

S-Corps again report profit and loss on a separate return and generally do not pay Federal tax, the net income is reported on the owner's return.
An LLC can also elect via an 8832 to be taxed like a corporation.

the profit and loss goes on the business return (1120) and the BUSINESS pays tax. When it pays the owners, it pays them via salary (w-2's) and distributions are taxed like dividends (Sch B).
Back to the Partnership, under tax law some important distinctions:

General partner - has risk, pays tax on profits, or claims losses on returns

Limited Partner- has limited risk, pays tax on profits, losses are claimed only when there other are passive gains
Being actively engaged in your business means you get to claim the losses of your business on your personal return.

This is important.

let's so thru a scenario
You run a business that reports a tax loss from:
Sch C on your 1040
General Partnership
Active member LLC (S-Corp) [will also have W-2 income]
Active officer (S-corp) [will also have W-2 income]
Assume $25K salary above

and your spouse makes $65,000
The way the IRS views it your active business losses are claimed in the year they occur against your personal income and your spouse's too when a joint return is filed.
Salary $65K spouse
add
Salary $25K
LESS
Business (loss)
Total(line 21 on a 2017 return) {which is in the news}
If Line 21 was +, proceed with other deductions and calculate the tax if taxable income still positive

If Line 21 was -, this generally and historically was your Net Operating Loss and you would either carry the balance backwards to the prior taxable year or forward.
Is this pretty clear? Lose money is a business you're active in you can claim losses against other income wages, int, royalties, etc and if the losses are big enuf carry the unused part of the losses forward to future years.

Now on to Depreciation
The IRC allows the claiming as an expense the cost of purchasing a building. This expense is called deprecation. Deprecation is further broken down into useful lives. A residential building as a useful life of 27.5 years. A commercial property has a useful life of 39 years
Dont confuse a commercial mortgage with a commercial property. A 16 unit building may be financed by a commercial mortgage but is a residential building for tax purposes.
So if you buy a residential building and land for $30M with the cost of the land being $2.5M, leaving the building valued at $27.5M, you can claim $1M in deprecation expense a year over the next 27.5 years.
Hey taxman I can't wait 27.5 years to write off this whole building, it's producing cash flow and I want to claim more expense!

Let me introduce you to the Cost Segregation Study!
From Wiki - It's the use of professionals to will divide a building up into it's component parts and you can claim the allocated cost of these parts according to their shorter than 27.5 year useful life. Thus get a sooner, larger depreciation expense!
You dont have to be a math genius to figure out that by breaking 1 building that is depreciated over 27.5 years, into a group of assets that are depreciated over 5, 7, 15, and 27.5 years that more expense will be claimed sooner, thus allowing that sweet rent income to go untaxed
If you had the property portfolio of Trump, wouldnt you be doing the same?
Now back to those K-1's I mentioned: what does one look like? Where do I see income?
where does that go on a 1040?
The BIG action on Trump's personal return is Sch E page 2. What is highlighted will be repeated over and over for all of his entities that he reports income on. There is also some action in Part 3 for the Trust his dad set-up that Trump has some benefit of.
His personal return shows no business detail and specific activity, just shows his net + or - from business operations and then sums

which is then reported on page 1 of the 1040 on line 17.
this is the basic explainer. There is more complexity here but I wanted to get this out and help ppl w/o a tax background understand some things that can and will be obfuscated.
I can go on further, but truth be told, I didnt even READ the NYT article. Just built this thread based on my knowledge of RE tax clients and mechanics of tax returns. now let me go read an article on his taxes that doesnt show me any documents.
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