You loved the 5% dividends from T (AT&T stock). You bought it (and only it) for your portfolio. So you've been feasting on that 5% for a long time. You loved it so much that you dipped into margin to buy more. That is, you had $10 million worth of T, paying you $500k a year in dividends. But the you bought another $5 million of it, on margin, so now you have $750k a year in dividends...but you also now have margin expenses on that $5 million of 2%, or $100k a year.
Your gross investment income is $750,000, but after that $100,000 in margin expenses, your net investment income (pre-tax) is $650,000.
Yeah, that tax thing? That's on you, bud.