DENVER (AP) — The leak of some of Donald Trump’s tax returns highlights enormous disparities in the tax code between high-income businesses and individuals and everyone else that may have allowed the Republican presidential nominee to avoid paying federal income taxes for nearly 20 years.

Trump claimed more than $900 million in losses in 1995,  enough to legally reduce his tax bill to zero for as many as 18 years, the New York Times reported on Sunday after receiving three pages of what appeared to be Trump’s tax returns filed in three states that year. Trump has broken with precedent and refused to release his tax returns during his presidential campaign, making it impossible to fully assess his finances and history of tax payments. But the 1995 loss likely lowered his future payments significantly or eliminated them altogether, because provisions in the tax code let businesses deduct losses from future income, decreasing the amount they and their owners will owe to the federal government in coming years.

Vermont Sen. Bernie Sanders told CNN on Sunday that Trump’s taxes “are exactly why so many millions of Americans are frustrated, they are angry, they are disgusted at what they see is a corrupt political system in this country.” Tax experts said the self-proclaimed democratic socialist may be onto something.

“The tax code treats very rich people who own businesses differently from the way it treats everyone else,” said Neil H. Buchanan, an  economist and tax law professor at George Washington University, noting that people can’t deduct losses on their homes even when they sell them for less than the purchase price.

During last week’s debate, Trump said he was “smart” for not paying taxes during a couple of years in the early 1990s. Buchanan and others said it’s more about Trump’s income than his intelligence.

“You can be middle class and be 10 times smarter and not be able to do the things he did,” Buchanan said.

The tax code allows this differential treatment — and other loopholes — to spur investment and job creation, said Howard Gleckman of the nonpartisan Tax Policy Center. The problem, he added, is that some of these loopholes are nonproductive tax shelters and the real estate industry is notoriously full of them.

Without access to Trump’s complete tax returns and those of his businesses, it’s impossible to know how he counted his losses in 1995. He had just finished a rough patch of business deals, including a failed airline and major losses at three Atlantic City casinos. But real estate companies can also count interest payments and depreciation of their holdings as shortfalls even if they have not actually lost cash on a property, a provision that tax experts argue lets them use paper losses to avoid paying their fair share of federal taxes.

“The real estate industry is built on tax subsidies,” Gleckman said.

Trump has argued that given his history, he’s best equipped to clean up the tax system. “I know our complex tax laws better than anyone who has ever run for president and am the only one who can fix them,” he tweeted early Sunday. He’s vowed to simplify the tax code, though some experts say Trump’s tax plan may create even more loopholes for businesses.

Bob McIntyre of the liberal Citizens for Tax Justice argued that the tax code needs to remain complicated because people like Trump keep trying to find ways to avoid the simple requirement to pay their fair share.

“The complexity comes from trying to stop people who have found ways around the simplicity,” McIntyre said.

One example comes from the real estate industry rules that Trump may have used to lower his tax burden. The 1986 tax reform wiped out many loopholes but preserved the ones for real estate investors after the industry lobbied furiously, he recalled.

“These are loopholes not because Congress figured them out, but because the companies lobbied for them,” McIntyre said. Modern-day examples are provisions that allow Apple, Google and other companies to avoid paying federal taxes by stashing profits in off-shore subsidiaries.

Alan Cole, an economist at the conservative Tax Foundation, argued that it’s incorrect to see the tax code as rigged against regular taxpayers. He noted that wealthy individuals still pay a huge share of federal income taxes — the top 1 percent of earners pay 38 percent of the nation’s total federal income taxes. And he argued that it’s dangerous to extrapolate from the tax returns of a man who called himself “the king of debt.”

“Turning this specific (and remarkable!) tax return into a general comment on the state of the tax system would be crazy,” Cole wrote in an email. “How many people do you know who lost a billion dollars? Show of hands?”