Donald Trump fancies himself a financial whiz and an original thinker, but his tax plan—characteristically vague though it is—runs up against the same problems faced by Jeb Bush and many other would-be tax-cutters and repeats their errors: It is nearly impossible to cut federal income taxes in a way that primarily benefits low-income Americans, because high-income Americans pay most of the federal income taxes.

The 2.4 percent of households with incomes in excess of $250,000 a year pay about half of all federal income taxes; the bottom half pays about 3 percent. It is not only the case that low-income Americans pay much more in payroll taxes than in income tax—that’s the case for all taxpayers save those in the top 20 percent of incomes. But we are committed to our national superstition that these Social Security and Medicare taxes are some sort of “contribution” to a retirement fund—they are no such thing—which means that serious payroll-tax reform rarely is on the agenda.

The centerpiece of Trump’s proposal is a zero income-tax rate for households with incomes up to $50,000 for married couples and $25,000 for individuals. Zeroing out income taxes for households at $50,000 and under sounds like a program aimed at the middle class and lower-income households, but it isn’t, really, because of how tax brackets work: Setting the rate at zero on the first $50,000 is a tax cut for households making $48,000, true, but it’s also a tax cut for households making $100,000, which would under the Trump plan pay $0.00 on their first $50,000 in income. For an unmarried taxpayer with no dependents earning $22,000 a year, Trump’s proposal represents about a $700/year tax cut; for a married couple earning $200,000, that’s going to be a much bigger tax cut, more than $6,500 a year. (Which is to say, the $1,845 they’d have paid on the first $18,450 of AGI plus the 15 percent they’d have paid on the amount between $18,451 and $50,000, plus the difference on the lower brackets on the rest. As always, check my English-major math.)