Having crunched the numbers on Jeb Bush and Donald Trump's tax plans, the Tax Policy Center — one of the only nonpartisan economic think tanks respected on both sides of the aisle in Washington — is out with an analysis of the tax plan of establishment favorite Marco Rubio.

Rubio's plan sticks out for focusing less on cutting the top rate (his is 35 percent to Bush's 28 and Trump's 25) than on expanding tax breaks, especially for families with children, and on exempting investment income from taxation. In that way, it's quite different, and more radical, than Bush or Trump's offerings.

But it's similar to them in price tag and in progressivity. Rubio's plan would cost the government $6.8 trillion in lost revenue over 10 years, TPC concludes, and would increase the deficit by $8.2 trillion once interest payments are taken into account. That's basically identical to the cost of Bush's plan, and significantly less than Trump's $9.5 trillion/$11.2 trillion proposal. And like both of their plans, it concentrates its benefits heavily among the richest Americans:

The analysis finds that the poorest fifth of taxpayers would get $232 back, a 1.3 percent boost in after-tax income. By contrast, the top 1 percent would get $204,995 (8.9 percent of income) back, and the top 0.1 percent would get $1,122,110 (11.5 percent). The overwhelming majority of the plan's cost (71.1 percent) goes to helping the richest fifth of taxpayers; 40.3 percent goes to the top 1 percent alone.

The estimated benefit to rich taxpayers is similar to that from previous analyses by the left-leaning Citizens for Tax Justice and right-leaning Tax Foundation.

Why Marco Rubio wouldn't help the poor as much as he claims

Rubio has insisted that his plan offers big benefits to low-income families, and a key part of that pitch has been his creation of a new refundable tax credit, worth $2,000 for individuals or $4,000 for couples, to replace the standard deduction and personal exemption. But this is not quite the massive break for poor families that Rubio insists it is.

The Tax Foundation and CTJ both assumed that this tax credit would be fully refundable: Literally all adults in America would get $2,000, no questions asked, regardless of whether they worked or had a positive tax liability or whatever. In other words, they assumed that Marco Rubio wanted to propose a small basic income.

Unsurprisingly, this turned out to be a very progressive policy. The Tax Foundation concluded Rubio's plan would raise incomes of the poorest 10 percent of tax filers by 44.2 percent, while CTJ found it would increase incomes for the poorest fifth of filers by 13.9 percent. While the largest monetary benefits still went to the richest, the biggest gains in percentage terms went to the poor. This was something Rubio loudly trumpeted in an October CNBC debate, insisting, "The greatest gains, percentage-wise, for people, are gonna be at the lower end of our plan."

The problem is that after the Tax Policy Center's Len Burman figured out this was what Rubio was doing, I emailed the senator's staff; they clarified that they had no intention of actually proposing a basic income, saying, "Rules would be tailored to ensure that our reforms would not create payments for new, non-working filers."

Unfortunately, the Rubio campaign didn't clarify what these rules would be when the Tax Policy Center asked them. So TPC made an assumption: The credit would be refundable against payroll taxes, but not beyond that. So let's say I make $10,000 a year. Because of the earned income tax credit, I already probably am not paying any taxes, and in fact will be getting a refund. But I'm paying payroll taxes: 7.65 percent, or $765, between both Social Security and Medicare. So TPC assumed that I couldn't get the whole $2,000 credit back, but I could get up to $765 of it.

This is an approach Rubio already used elsewhere in his tax plan. He and Sen. Mike Lee (R-UT) proposed adding a new $2,500 child tax credit on top of the existing $1,000 one. The new credit, like the existing one, would be partly refundable, but unlike the current credit it would be refundable only up to one's payroll tax liability. TPC just carried over that existing restriction to the other refundable credit Rubio is proposing.

Long story short: Once you add this restriction, the gains to poor families shrink drastically. CTJ assumes the poorest fifth of Americans would get $2,168 each on average; the TPC estimate is about a tenth of that, or $232.

Now, Rubio's camp could dispute this by arguing TPC's assumption is unfair and that their rules are different. But it's on them to think of a more plausible way to restrict the credit to working people. And basically any way they choose is going to have a similar effect of reducing benefits for the poor.

By the way, this also helps explain why CTJ's estimated cost for Rubio's plan ($11.8 trillion) is so much bigger than the Tax Policy Center's. Giving away $2,000 to every household in America is really, really expensive; even the more limited version TPC evaluated costs $4.1 trillion over 10 years. If you make it fully refundable, as CTJ assumed, that adds even more to the price tag.

The Tax Foundation found a much lower cost than TPC: $4.1 trillion. TPC explains this by noting that a) since the Tax Foundation analyzed the plan, Rubio changed it slightly from the version he promoted with Mike Lee, most notably adding a 25 percent bracket between the 15 and 35 percent ones, which increases the cost substantially; and b) the Tax Foundation assumed that Rubio's plan would be fully phased in, including the part that lets businesses fully deduct the cost of their investments the year they're made, whereas TPC assumed it would be phased in gradually, increasing the cost.

The most daring part of Rubio's plan: a VAT by another name

Marco Rubio has repeatedly attacked the tax plan of his rival Ted Cruz for including a value-added tax (VAT), a kind of sales tax popular in Canada, Japan, and Europe. Cruz has preposterously denied he's proposing a VAT, but he definitely is, and Rubio's Super PAC has hammered him on it, calling it "Canadian," just like Cruz himself:

But as the TPC analysis notes, Rubio goes a long way toward transforming the income tax into a version of a VAT called an "X tax." Invented by the late economist David Bradford and championed loudly by American Enterprise Institute fellow and tax expert Alan Viard, the X tax imposes a VAT on businesses but lets them deduct the cost of wages. Then it taxes wages progressively while not taxing investment income at all. So it's taxing the same base as a VAT but doing it more progressively.

Rubio's plan, put together, moves the US much closer to an X tax. Letting businesses immediately deduct investments and other expenses, as Rubio proposes, turns the corporate tax into the business side of an X tax; Rubio also wants to totally eliminate taxation of long-term capital gains, dividends, and interest, which moves the personal income tax much further toward just taxing wages, as in an X tax. As TPC notes, there are still some differences — a pure X tax wouldn't tax short-term capital gains, while Rubio does, and a pure X tax would set the corporate rate significantly higher than Rubio does — but it's very close.

X taxes, particularly Rubio's version, are hardly perfect. They let rich people who get most of their income from investments totally off the hook — Mark Zuckerberg and Bill Gates would probably never pay a dime of federal income tax again — and create a massive incentive to shelter wage income by passing it off as investment money. Another model of progressive consumption tax championed by Cornell's Robert Frank, which simply adds an unlimited savings deduction to the existing income tax, would get around these problems.

It's also worth noting that while many economists think consumption taxes like the X tax or VATs are better for economic growth than income taxes, this view isn't universal. Recent research finding that tax incentives to save don't promote savings particularly well and that the 2003 tax cut in dividends didn't really boost the economy has also cast doubt on the general case for consumption taxation.

But the fact that Rubio comes closer than any candidate still standing to eliminating income taxation altogether and just taxing consumption is pretty notable, regardless of your stance on the matter. It's a more ambitious transformation than anyone else is proposing — and, by exempting capital income, probably a better one for the rich as well.

Update: When asked about the TPC analysis in South Carolina, Rubio shot the messenger (transcript via the Rubio campaign):