By Ken Thomas and Richard Rubin 

WASHINGTON -- Vermont Sen. Bernie Sanders released a decade's worth of his tax returns Monday, showing an annual income that exceeded $1 million in 2016 and 2017 following his first presidential campaign.

Mr. Sanders and his wife, Jane O'Meara Sanders, in 2018 paid total federal taxes of $145,840 on $561,293 in adjusted gross income. Their effective tax rate was 26%.

The couple's adjusted gross income was more than $1.1 million in 2017 and more than $1 million in 2016, helped by the proceeds of his 2016 book, "Our Revolution," which chronicled his presidential primary bid against Hillary Clinton.

More recently, Mr. Sanders earned $391,000 in book royalties from his 2018 book, "Where We Go From Here."

His campaign said the couple's income increased in 2016 due to advances and royalties from "Our Revolution," which it said had been translated into five languages.

The tax records also reflected proceeds from a youth version of "Our Revolution," along with the publication of "Where We Go From Here," and an advance on a book currently being written by Ms. Sanders.

Mr. Sanders said in a statement that the tax returns "show that our family has been fortunate," and he considered paying more in taxes in recent years "both an obligation and an investment in our country."

"I will continue to fight to make our tax system more progressive so that our country has the resources to guarantee the American dream to all people," he said.

Mr. Sanders became the sixth 2020 presidential candidate to make his personal tax returns public. Democrats have released years of their tax documents during the primary, seeking to promote transparency and highlight President Trump's unwillingness to release his returns.

During his 2016 campaign, Mr. Trump said he would release his tax returns but has refused to do so, breaking a 40-year tradition of voluntary disclosure for major-party nominees.

California Sen. Kamala Harris released 15 years' worth of tax returns on Sunday. She followed Sens. Kirsten Gillibrand of New York, Elizabeth Warren of Massachusetts and Amy Klobuchar of Minnesota, along with Gov. Jay Inslee of Washington state, who have posted at least a decade of their tax returns online.

Other candidates are expected to soon follow suit, including former Rep. Beto O'Rourke of Texas, New Jersey Sen. Cory Booker and South Bend, Ind., Mayor Pete Buttigieg.

Mr. Trump has cited a continuing audit by the Internal Revenue Service, which routinely audits presidential tax returns. There is nothing, however, that would bar Mr. Trump from voluntarily releasing his tax returns even if he is under audit.

House Democrats have set an April 23 deadline for the IRS to turn over Mr. Trump's tax returns. Under the tax code, the chairman of the House Ways and Means Committee can request any taxpayer's returns and the Treasury Department "shall furnish" them. The dispute could wind up in court if the Trump administration asserts that Congress doesn't have a legitimate legislative purpose for the request.

The documents Mr. Sanders released Monday show that he and his spouse paid total federal taxes of $343,882 in 2017 for an effective tax rate of 30.3% and $372,368 in 2016 for an effective tax rate of 35%.

The senator's tax returns, covering 2009 to 2018, show an income that fluctuated between more than $200,000 a year to more than $300,000 annually before his presidential campaign.

The couple reported an adjusted gross income of more than $300,000 in 2009-2011 but their income dipped in the following three years.

Ms. Sanders received a $200,000 severance package after resigning from Burlington College in the fall of 2011, according to a 2012 audit of the school's finances. She had served as the small liberal arts school's president since 2004.

As president, she had secured loans to purchase a $10 million lakefront property for the school. But the school's fundraising and enrollment never matched Ms. Sanders's projections, according to two former Burlington College trustees who said the board asked Ms. Sanders to resign. The 44-year-old school collapsed under the weight of its debt, eventually closing in May 2016.

Ms. Sanders declined in a recent interview to discuss her tenure at Burlington College.

It wasn't immediately clear whether Mr. Sanders benefited from the 2017 tax cut that he voted against because the couple's income went up and down so much from year to year. Mr. Sanders's 2018 return said it is self-prepared, as opposed to being prepared by an accountant.

In 2018, they paid nearly $13,000 in mortgage interest and more than $65,000 in state and local taxes and donated $18,950 to charity. In 2017, they donated $36,300 to charity, though the documents didn't list the recipients of those donations. In 2016, the couple donated $10,600 to charity.

Also in 2016, the couple claimed a tax credit of nearly $6,000 for installing "solar electric property" at a home.

In 2017, they reported having a financial interest in a foreign bank account and then filed an amended return saying they did not. (They said they had inadvertently checked yes.)

Mr. Sanders said in late February that he would soon release his tax records, saying in a town-hall meeting broadcast on CNN at the time, "Our tax returns will bore you to death." He has noted that Ms. Sanders prepares the family's tax returns. In 2009, for example, the tax return was handwritten.

During his 2016 primary race against Mrs. Clinton, Mr. Sanders released a seven-page federal tax return from 2014 but declined to release earlier tax records. Mrs. Clinton released decades of her tax returns dating back to 1977.

The 2014 filing released by Mr. Sanders at the time showed that most of his family's income came from his Senate salary and Social Security benefits.

Mr. Sanders has spent nearly the past four decades in public office. He was the mayor of Burlington, Vt., from 1981 to 1989, and served in the U.S. House from 1991 to 2007. He has been in the Senate since 2007.

Julie Bykowicz

contributed to this article.

Write to Ken Thomas at ken.thomas@wsj.com and Richard Rubin at richard.rubin@wsj.com

(END) Dow Jones Newswires

April 15, 2019 18:34 ET (22:34 GMT)