In that campaign, Mr. Sanders disclosed his tax return for only one year, 2014, which showed that he and his wife had an adjusted gross income of $205,271, largely from his Senate salary and Social Security benefits.

More recently, Mr. Sanders has come under criticism for his expanding personal wealth. A post on the website ThinkProgress last week called Mr. Sanders’s millionaire status “very off-brand and embarrassing,” and a video suggested he had stopped referring to “millionaires” after he became one himself. The website is run by the Center for American Progress Action Fund, the sister organization of the Center for American Progress, a liberal think tank.

On Saturday, Mr. Sanders fired back, accusing the think tank of “using its resources to smear” him and other progressive presidential candidates. The think tank was founded in 2003 by John D. Podesta, a close Clinton ally who served as Mrs. Clinton’s campaign chairman in 2016. (The editor in chief of ThinkProgress said in a statement that the site was an “editorially independent journalistic entity.”)

[On Fox News, Mr. Sanders rejected the idea that his wealth was proof of the “American dream.”]

Tax returns released by other Democratic presidential candidates have shown that they also earned more than a vast majority of American households in recent years. Senator Kamala Harris of California and her husband reported an adjusted gross income of about $1.9 million last year, while Senator Elizabeth Warren of Massachusetts and her husband had $846,394 in adjusted gross income.

Former Representative Beto O’Rourke of Texas also disclosed 10 years of tax returns on Monday, though not his 2018 return. He and his wife, Amy O’Rourke, reported $366,455 in adjusted gross income on their 2017 return.

The couple reported donating $1,166 to charity that year, just three-tenths of 1 percent of their income, though it is possible they made other donations not listed on their personal return.

The filings showed the extent to which the O’Rourkes have benefited financially from family wealth. Mr. O’Rourke’s income was boosted over the years through his interest, passed to him by his parents, in a shopping mall and an apartment complex. Ms. O’Rourke collects dividends and interest from family partnerships established by her father, the real estate investor William D. Sanders (no relation to Bernie Sanders). In some years, that dividend and interest income contributed over $100,000.