Sen. Bernie Sanders, who is seeking the Democratic presidential nomination. (AP Photo/Cliff Owen)

Sen. Bernie Sanders (I-Vt.), who rails against the “billionaire class” on the presidential campaign trail, reported relatively modest income last year: just more than $200,000 on a tax return filed jointly with his wife.

The vast majority of the couple’s income came from Sanders’s $174,000 Senate salary and Social Security benefits that both he and his wife, Jane, a former college president, receive.

Sanders, who has been rising in the polls in his bid for the Democratic nomination against Hillary Rodham Clinton, voluntarily released the first few pages of his 2014 federal and Vermont tax returns Tuesday at the request of The Washington Post.

[In Bernie Sanders, an unlikely — but real — threat to Hillary Clinton]

He did so on the same day that Republican hopeful Jeb Bush made available 33 years of tax returns. Those showed that Bush had made $29 million since leaving the Florida governor’s office in 2007, including $7.3 million in adjusted gross income in 2013. Bush did not release the tax returns for 2014.

Clinton has yet to release any tax returns, but her income in recent years appears to have vastly exceeded that of Sanders. Clinton has made millions in public speaking fees and book royalties, according to disclosures she has made.

[Clintons have made more than $25 million for speaking since January 2014]

According to his tax forms, Sanders and his wife paid $27,653 in federal income tax and another $7,903 in Vermont income tax last year. The couple paid an effective tax rate of 19.6 percent on their federal taxable income of $140,994.

Sanders reported receiving $156,441 from his Senate job, after contributions to a savings plan and health insurance. The couple reported receiving another $46,213 in Social Security benefits, of which $39,281 was taxable.

Sanders also reported income of $4,982 from the pension he receives having been mayor of Burlington, Vt., in the 1980s. And his wife had another $4,900 in compensation for sitting on a commission devoted to the management of low-level radioactive waste disposal.

On a separate disclosure form required of presidential candidates, Sanders reported having between $25,000 and $65,000 in credit card debt at some point during the past year.

Sanders spokesman Michael Briggs said the debt was related to weddings of a daughter and niece and that Sanders and his wife had since paid the balance on the two credit cards down to zero.

“Like a lot of Americans, they use credit cards to pay everyday expenses,” Briggs said.

[Sanders says he’s no ‘Johnny-come-lately’ to big issues of the campaign]

On the disclosure form, which was filed May 29 with the Federal Election Commission, Sanders also noted having received $1,017.42 in 2014 from the publisher of a book that includes the text of a nearly nine-hour filibuster he conducted in 2010. The book is titled “The Speech: A Historic Filibuster on Corporate Greed and the Decline of Our Middle Class.” Sanders also reported receiving an $850 honorarium for having appeared on HBO’s “Real Time with Bill Maher.”

The money from the book and the television appearance were both donated to charity, Briggs said. Sanders donated another $8,350 to charity last year, Briggs said.

On his Vermont tax return, Sanders made a total of $150 in voluntary contributions to support four causes: at-risk children; endangered wildlife; military veterans; and the environment.

On his federal return, Sanders -- who advocates for public financed elections -- elected to support the presidential election campaign fund.

A spokeswoman for another Democratic hopeful, former Maryland governor Martin O’Malley, said he plans to release his tax returns shortly. Like Sanders, O’Malley and his wife, a district court judge in Baltimore, are expected to show relatively modest income. O’Malley has also incurred debt in recent years related to two of his four children attending college, aides say.