In perhaps the single most astounding passage of her campaign memoir What Happened, Hillary Clinton reveals a campaign proposal she formulated with staffers but never actually released: a universal basic income for Americans, funded by carbon and financial transaction taxes.

"I wanted very much to convey a commitment to trying to figure ways to raise incomes," she said in an interview with Vox's Ezra Klein. "The Alaska model where they write a check to every single Alaskan every year based on a formula about the oil and gas revenues was really intriguing to me.”

Here’s the relevant passage of the book, on page 239:

Before I ran for President, I read a book called With Liberty and Dividends for All: How to Save Our Middle Class When Jobs Don’t Pay Enough, by Peter Barnes, which explored the idea of creating a new fund that would use revenue from shared national resources to pay a dividend to every citizen, much like how the Alaska Permanent Fund distributes the state’s oil royalties every year. Shared national resources include oil and gas extracted from public lands and the public airwaves used by broadcasters and mobile phone companies, but that gets you only so far. If you view the nation’s financial system as a shared resource, then you can start raising real money from things like a financial transactions tax. Same with the air we breathe and carbon pricing. Once you capitalize the fund, you can provide every American with a modest basic income every year [emphasis Vox’s]. Besides cash in people’s pockets, it would also be a way of making every American feel more connected to our country and to one another—part of something bigger than ourselves. I was fascinated by this idea, as was my husband, and we spent weeks working with our policy team to see if it could be viable enough to include in my campaign. We would call it “Alaska for America.” Unfortunately, we couldn’t make the numbers work. To provide a meaningful dividend each year to every citizen, you’d have to raise enormous sums of money, and that would either mean a lot of new taxes or cannibalizing other important programs. We decided it was exciting but not realistic, and left it on the shelf. That was the responsible decision. I wonder now whether we should have thrown caution to the wind and embraced “Alaska for America” as a long-term goal and figured out the details later.

Let’s be clear: “Alaska for America” would mean, just like the actual Alaska Permanent Fund, establishing a universal basic income. And Clinton understands this, even calling the benefit a “basic income.”

The Alaska Permanent Fund is a state-owned investment fund established using oil revenues. It has, since 1982, paid out an annual dividend to every man, woman, and child living in Alaska. In 2015, with oil prices high, the dividend totaled $2,072 per person, or $8,288 for a family of four. In 2016 it was cut down to $1,022 due to money being diverted to other purposes, and in cheaper gas years it can dip into the $800 to $900 range. But regardless, it is the only program in the US — and one of the few in the developed world — offering cash to every citizen, no strings attached.

And it works. It’s tremendously popular, supported by Republican and Democratic governors alike (Sarah Palin was a big fan during her time in office), and research by University of Chicago economist Damon Jones and University of Pennsylvania economist Ioana Marinescu has found that the dividend doesn't discourage work. It appears to cause a small increase in the share of people working part time, but Jones and Marinescu conclude it has no overall effect on the share of the population working. Indeed, the part-time work boost could come from people entering the workforce anew.

This is a less politically appealing comparison than Alaska, but Iran has a similar program. While winding down the country’s extensive oil subsidies for citizens, President Mahmoud Ahmadinejad implemented a flat cash dividend, paid out to every man, woman, and child in the country. It's been dialed back a bit since, but it also has shown few negative effects. A study examining the Iranian basic income’s effect on work concluded that “the program did not affect labor supply in any appreciable way.” That’s especially astounding given the size of the benefit: In 2011, when it was introduced, it provided about 29 percent of the median household income on average. In the US, that would mean paying out $16,390 to the average family.

And in both the Alaskan and Iranian cases, the benefits are provided with no increase in household taxes, making the program particularly attractive. Taxing energy is a pretty efficient source of funds.

Peter Barnes, the entrepreneur and environmentalist from whom Clinton borrowed the idea, has actively pushed for a similar model of funding basic income in the US as a whole (he prefers the term “base income,” to reflect that the amount of money being transferred wouldn’t be enough for someone to live on). In his variation, instead of using oil revenues, you’d tax pollution and financial speculation, which he argues is similarly efficient and also reflects a sense that the climate and the financial system are shared resources.

“It is an answer — perhaps the answer — to long-term economic stagnation, a trickle-up form of Keynesianism that would stimulate our economy through increased household spending,” Barnes writes in the Boston Review. “Moreover, if funded by fees on unproductive activities such as pollution and speculation, it would help solve two other deep problems of twenty-first-century capitalism: climate change and financial instability.”

So why didn’t it happen? From Clinton's telling, the proposal was abandoned due to one of the recurring sticking points with basic income plans: They cost a lot of money. Clinton wanted to provide a "meaningful" dividend, and didn't think she could do it with a realistic set of new taxes.

"We dug deep, tried to explain it to some people, and it just was hard for people to grasp what we were talking about because most Americans in the Lower 48 didn’t have any idea about what was going on in Alaska," she elaborated to Vox’s Ezra Klein.

This is an understandable conclusion. A basic, or even just “base,” income was too far out there for Bernie Sanders to endorse during the 2016 primary; even the leftmost candidate in the race thought it was either undesirable or too hard to explain and pitch to Americans.

But the fact that a major-party presidential nominee seriously considered basic income as a proposal is nonetheless a huge sign of the idea’s progress and increasing influence.