US Senator Bernie Sanders, who has made income inequality a hallmark of his presidential campaign, earned with his wife, Jane, about US$566,000 last year and US$1.15 million in 2017.

The US$1.7m ($2.5m) puts them in America's highest income brackets, according to tax returns released by the presidential candidate today.

Much of Sanders' income came from books he has written about his democratic socialist platform, which includes a call for higher taxes on the wealthiest Americans.

Sanders has become wealthier, in part, by cashing in on his status as a presidential candidate. In 2014, prior to his first presidential run, he reported an income with his wife of about US$206,000, according to his tax returns.


Since then, he has written two campaign-oriented books: Our Revolution in November 2016 and Where We Go From Here in November 2018. The impact of his book contracts is most evident in Sanders' return for 2017, when he and his wife reported wages of US$139,549 and business income - most of it from books - of US$961,784.

That squares with a financial disclosure report that Sanders filed last year as a senator, which showed that he earned US$880,000 in royalties from book deals.

The 2018 returns show that the Sanders contributed about US$19,000 to charity out of their income of US$566,000, or 3.35 per cent. The couple gave US$36,300 to charity in 2017.

The Sanders campaign said those rates do not reflect charitable proceeds given from one of his books, which he did not deduct from his taxes. The campaign did not say how much was given in that case.

Sanders said that: "These tax returns show that our family has been fortunate. I am very grateful for that, as I grew up in a family that lived paycheque to paycheque and I know the stress of economic insecurity. I consider paying more in taxes as my income rose to be both an obligation and an investment in our country."

The Sanders campaign said in a press release that he paid 26 per cent effective tax rate in 2018.

Daniel Shaviro, a New York University School of Law professor of taxation, who examined the 2018 return at the request of the Washington Post, said the return was straightforward.

"He didn't do a whole lot, economically or tax-wise, other than earn his Senate salary, Social Security income, and book royalties, as well as paying state and local taxes and giving about US$19,000 to charity," Shaviro said. "This clearly is not the tax return of someone who does either a lot of tax planning or complex investing."

The earliest return released yesterday, for 2009, was done by hand, which may indicate that the Sanders did the taxes themselves. It showed they had total income of US$314,742. All of the other returns have typed entries.

There is no requirement that presidential candidates release their tax returns, but many have done so by tradition. Sanders faced pressure to release his returns this year as Democrats have increasingly made an issue of US President Donald Trump's refusal to release returns.

Trump said during the 2016 campaign that he would release his returns after an audit was completed. But after the House Ways and Means Committee requested them, Trump's acting chief of staff, Mick Mulvaney, said earlier this month that Trump would "never" turn them over.

Sanders' personal wealth has come under heightened scrutiny in recent weeks. At a campaign stop in Gary, Indiana, a reporter asked Sanders whether his millionaire status was at odds with his populist economic message.

"I don't think so," Sanders replied. "I didn't know it was a crime to write a good book."

He said that his view has long been that the wealthiest Americans ought to pay more taxes. "If I make a lot of money, you make a lot of money, that is what I believe," said Sanders.

He added, "I don't apologise for writing a book that was number three on the New York Times bestseller [list]."

As a senator, Sanders has been required to release a financial disclosure statement, but the information in that is much more limited than the data in a tax return. For example, the disclosure form only requires that income and debts be described in wide ranges, and does not report the value of real estate.

Bernie and Jane Sanders have three homes, one in Burlington, a second in Washington and a third, on a Vermont lake front. Sanders was first elected to the Senate in 2006 and served in the House for 16 years before that.

Former New Hampshire Democratic Party chair Kathy Sullivan said that while she does not see a problem with Sanders' financial status squaring with his commitment to curbing income inequality, she was struck by the way he handled questions about his wealth.

"I don't think it's a problem that someone has been successful in the private sector," said Sullivan, who supported Hillary Clinton in the 2016 primary. "He seemed defensive about it and I don't think he should be."

The perception of a contrast between Sanders' wealth and his rhetoric has become a campaign issue on both the left and the right.

Fox News mocked him on its website in a February story headlined: "Lifestyles of the rich and socialists: Bernie Sanders has 3 houses, makes millions."

It questioned whether "the self-described democratic socialist's high-end income, multiple houses and fondness for air travel" are at odds with his rhetoric about income inequality.

A liberal website, ThinkProgress, earlier this month posted a video about what it called "Bernie's millionaire problem." It included clips of Sanders criticising the influence of "millionaires and billionaires" alongside a chart showing how he became a millionaire through his books sales.

ThinkProgress is affiliated with the Centre for American Progress, a liberal group, but says it is editorially independent. Sanders said he was subject to a "smear" by the group, which was founded by John Podesta, who chaired Clinton's 2016 campaign. Podesta did not respond to a request for comment.

Jodi Enda, the editor-in-chief of ThinkProgress, said in an interview that the Centre for American Progress does "not see the stories until they are online" and had nothing to do with the video.

"Nobody was trying to attack him," she said. "We were just stating the facts." She said the video would remain online.

Neera Tanden, president of the Centre for American Progress and a former adviser to Clinton, said in a statement that the video was "overly harsh."

A number of other Democratic presidential candidates have released tax returns in recent weeks.

Senator Kamala Harris yesterday released 15 years of tax returns, which showed that she and her husband earned about US$1.9 million in adjusted gross income in 2018.

Senator Elizabeth Warren earlier this month released a tax return that showed she and her husband earned about US$906,000 in 2018.

Senator Amy Klobuchar released 12 years of tax returns, showing that she and husband earned about $292,000 in 2017. Senator Kirsten Gillibrand and her husband earned about US$215,000 in 2018.

Governor Jay Inslee of Washington released 12 years of tax returns, showing that he and his wife earned US$202,912 last year.