A decade ago, in an essay for The New York Times, Warren Buffett disclosed that he had paid nearly $7 million in federal taxes in 2010. “That sounds like a lot of money," he wrote. “But what I paid was only 17.4 percent of my taxable income — and that's actually a lower percentage than was paid by any of the other 20 people in our office. Their tax burdens ranged from 33 percent to 41 percent and averaged 36 percent."

The words “taxable income" are doing a lot of work in that sentence.

Buffett owns a substantial number of shares in Berkshire Hathaway, the fabulously successful holding company he founded decades ago. As the company's shares have soared nearly every year, his wealth has grown by billions. Under the U.S. tax code, none of that is taxed until he sells shares at a profit.

A little math shows that Buffett's 17.4% rate meant he reported roughly $40.2 million in income in a year where Forbes said his wealth grew by $3 billion. His revelation made it possible to compare how much he was paying the government to the increase in the size of his fortune.

No one did so, and Buffett became something of a folk hero for calling for any increase in taxes.

When we obtained access to a trove of tax data on the richest Americans, it quickly became clear to our reporters that Buffett's comparison of his own tax rate to his employees' vastly understates the inequity of our tax system. Buffett is far from unique; the documents showed that the amount of money people like Michael Bloomberg, Jeff Bezos or Elon Musk reported to the IRS as income was infinitesimal when measured against their annual gains in wealth.

And so the first story in our “Secret IRS Files" series set out a new concept that makes more sense in our 21st century Gilded Age; we called it “the true tax rate." We compared the annual taxes paid by the ultrarich to their wealth gains to give readers a sense of how the system really works.

From 2014 to 2018, we pointed out, Buffett paid $125 million in federal taxes. As he said, that sounds like a lot. But according to Forbes, his riches rose $24.3 billion during that period, making his true tax rate 0.1 percent. In a detailed written response, Buffett defended his practices but did not directly address ProPublica's true tax rate calculation.

When we published this story, howls of rage rang out from the freewheeling corners of Twitter to the ornate offices on Wall Street. Some of the most irate critics wrote to me directly and demanded to know whether I was so @#$!@ stupid that I didn't understand the meaning of the word “income tax."

“This story, sadly, reeks with 'class envy,'" one angry reader wrote. “If this was intended to get clicks, you made your money." We're a nonprofit and our revenue from advertising adds almost nothing to our annual budget, but I understand this reader's larger point, which we noted in the story: The ultrarich are doing only what the current tax code invites them to do.

The debate intensified, and the White House-backed proposals on taxes advanced by congressional Democrats largely followed the traditional approach of raising rates on income. A separate bill introduced by Sens. Elizabeth Warren and Bernie Sanders to impose a 3% tax on all wealth above $1 billion is seen as having little chance of passing.

The reluctance to embrace a wealth tax is deeply rooted. The biggest donors to both parties would be hit hard by such a law. And as we pointed out in our initial story, the complexities of taxing wealth are not trivial. Several countries have tried and struggled to figure out a fair way to tax stock gains. Does an entrepreneur whose stock skyrockets in one year, and pays a big tax, deserve a rebate if his company's shares plummet the next year?

All of that said, we took note when White House economists issued a study that used publicly available data to estimate “the average Federal individual income tax rate paid by the 400 wealthiest American families' in recent years, determined using a more comprehensive measure of income." Their methodology was similar to ours, and their findings — that those families gained $1.8 trillion from 2010 to 2018 and paid 8.2% in taxes — are in line with what we found in the tax data.

The authors say their findings are evidence in support of President Joe Biden's plan for tweaking the existing system; the words “wealth tax" are not mentioned. They point to the administration's proposal to impose higher tax rates on stock dividends and on capital gains, the profit an investor reaps when selling a stock whose value has risen.

(The Biden administration has proposed getting rid of a provision in the tax code that shields heirs who inherit stock from paying capital gains tax on the growth in value that occurred before the shares were transferred.)

None of the proposed changes come close to addressing the biggest hole in the system, which is that an ultrarich person can live comfortably off gains in wealth while never selling a single share. As our initial story pointed out, the Buffetts and Bezos of the world can borrow against the value of their considerable holdings and live comfortably without selling stock or receiving any income from dividends, which new companies like Tesla and Amazon don't pay.

The strategy, known as “buy, borrow and die," allows the wealthy to amass fast fortunes, pay no taxes on those gains and pass on much of the wealth to their descendants.

Herb and Marion Sandler, the founders of ProPublica, made it clear from the outset that they hoped our journalism would spur real-world change. They were not particularly interested in stories whose biggest effect was that they had “started a conversation."

We still measure our success by tangible effects. But over the years, we have seen that the road to impact on very complex issues can begin by changing the conversation.

Lawmakers have said that some of the most egregious tax loopholes we've exposed, notably multibillion-dollar Roth IRA accounts, will be scrutinized as Congress takes up tax legislation in coming months.

There's no telling where the larger conversation about taxing wealth will lead. As the White House paper suggests, a new way of thinking about equality and taxation has taken center stage. Whether that ultimately results in change remains very much an open question.