Sen. Bernie Sanders, a leading candidate for the 2020 Democratic presidential nomination, released 10 years' worth of tax returns on Monday, showing the man who routinely derides "millionaires and billionaires" earned more than $1 million in income in 2016 and 2017.

The financial disclosure was highly anticipated, given Sanders only published his 2014 tax filings in 2016 when he contested the party's nomination against Hillary Clinton. The filings also show income generated by his wife, Jane Sanders, who was investigated for allegations that she, as president of Burlington College, overstated "confirmed" donation amounts when trying to secure a $6.7 million loan in 2010. The school closed in 2016 due to financial problems, and Jane Sanders was not charged by federal prosecutors over the claims.

According to the documents, the Sanders' adjusted gross income in 2018 was $561,293, they fell within the 26% marginal tax rate, and the couple donated 3.4% to charities, including senior centers, low-income organizations, educational entities, and environmental and housing advocacy groups.

In 2016, the Sanders had an adjusted gross income was $1,062,626, paid 35% in marginal taxes, and gave 0.99% to charity. In 2017, they made $1,150,891, owed 30% in marginal taxes, and donated 3.2% in charitable giving.

[Related: Bernie Sanders: 'I don't vilify' millionaires]

The independent senator from Vermont, who self-identifies as a socialist and whose White House bids have been underpinned by the argument that the economy is rigged to benefit the top 1% of earners in the country, sought to diffuse expected criticism in twin statements.

"The returns reflect that the Sanders’ primary sources of income over most of those years were Senator Sanders’ Senate salary and proceeds from his writing," the senator's campaign said in a "key details" section of the statement.

"In 2016, the Sanders’ income increased substantially due to advances and royalties from his best-selling book Our Revolution: A Future To Believe In, which has been translated into 5 languages and published in a number of countries," the statement added. "The youth version of Our Revolution, the publication of Where We Go From Here and an advance on a book currently being written by Jane Sanders, are also reflected in the tax filings."

The senator acknowledged on Monday the returns "show that our family has been fortunate."

"I am very grateful for that, as I grew up in a family that lived paycheck to paycheck and I know the stress of economic insecurity. That is why I strive every day to ensure every American has the basic necessities of life, including a livable wage, decent housing, health care and retirement security,” he wrote in a statement. “I consider paying more in taxes as my income rose to be 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.”

Last week, Sanders alluded to his wealth in an interview with the New York Times and urged President Trump to be similarly transparent about his assets. Referring to his book that was No. 3 on the New York Times bestseller list, Sanders told supporters that he "didn’t know it was a crime to write a good book."

The Vermont lawmaker currently sits in second place for the Democratic nomination, according to the latest RealClearPolitics polling average. He trails former Vice President Joe Biden, who has yet to announce a presidential run, by a little less than 10 percentage points.