Democratic presidential candidate and former vice president Joe Biden speaks at a campaign event in Sumter, S.C., on July 6, 2019. (Meg Kinnard/AP)

Joe Biden on Tuesday reported earning $15.6 million in family income over the past two years, making him the highest earner among the top competitors for the Democratic presidential nomination.

The vast majority of the former vice president’s income — which totaled $11 million in 2017 and $4.6 million in 2018 — came from book payments and speaking fees, according to newly released tax returns and financial disclosure forms required of federal office-seekers.

All told, the Bidens made nearly five times more in the past two years than the next- highest earner, Sen. Kamala D. Harris (D-Calif.), who with her husband earned $3.3 million. Sen. Bernie Sanders (I-Vt.) and Sen. Elizabeth Warren (D-Mass.) each took in about $1.7 million in family income.

The amount of wealth — with Biden at the top — comes amid a campaign that features a strong current of economic populism, with Sanders and Warren in particular making a case that the economy is rigged in favor of the rich.

The tax returns and financial disclosure statements Biden released Tuesday provided the first picture of the wealth he has accumulated since leaving a 44-year career in government.

A regular theme of his presidential campaign has been the fact that he was often the poorest member of the U.S. Senate during his tenure there, as determined by disclosure forms. For at least a decade, Biden repeatedly has described himself as “Middle Class Joe.”

His supporters argue that his hardscrabble upbringing in a middle class home in Scranton, Pa., still influences how he sees himself.

But since leaving office, he has benefited from an explosion of wealth. He gave 47 speeches, according to the new filings, with fees as high as $234,000. His speaking fees and book payments amounted to $10 million in 2017 and $3.2 million in 2018.

Biden was also a professor at the University of Pennsylvania, where he was paid $371,159 in 2017 and $405,368 in 2018.

Jill Biden, his wife, delivered 18 speeches that were noted in the financial disclosure forms, for which she earned more than $700,000. She also received a salary of more than $90,000 annually for her work as a professor at Northern Virginia Community College.

The Washington Post detailed last month how Biden’s standard of living has been enhanced since he left office in January 2017.

He has purchased a $2.7 million, 4,800-square-foot vacation house near the water in Rehoboth Beach, Del., to go along with his primary residence, the nearly 7,000-square-foot lakeside home he built more than two decades ago in Wilmington, Del.

Biden didn’t list a mortgage on his vacation home, an indication that he had paid off the $2.7 million residence in full. His 2017 tax returns showed that the couple took in $11,319 in rental income. That stemmed from an arrangement by which the Secret Service continued paying rent for a cottage on the property until his protection ended in mid-2017.

Biden also has been renting a 12,000-square-foot home in McLean, Va., that features five bedrooms and 10 bathrooms, marble fireplaces, a gym and a sauna. Biden’s campaign has declined to disclose details about the financial arrangement for the home, which is owned by Mark Ein, a well-connected, politically active donor who owns the Washington Kastles tennis team, the Washington City Paper, and Kastle Systems, which handles security systems for commercial office buildings.

Biden’s campaign would only say that the former vice president was paying “substantial monthly rent.” Zillow, the real estate site, estimates monthly rent for the home to be nearly $20,000.

Because he does not own the home, Biden did not have to disclose details about it in his financial disclosure forms or tax filings.

Biden’s previous financial disclosure, filed in 2016 and covering the year 2015, showed assets ranging from $303,000 to $1.115 million. His debts at that time ranged from $780,000 to $1.6 million, largely from a mortgage and a secondary loan on his primary residence.

Biden now has almost no debts listed. The only outstanding debts were loans against the cash value of life insurance policies, which Biden took out in 1983 and were valued at $15,000 to $50,000; and a line of credit, originally co-signed with his sons in 1989 for college expenses, that has been renewed every two years.

Biden’s assets have not increased as dramatically as his income. He has few large investments, but lists several bank accounts with significant cash in them. Two hold up to $250,000 and one holds up to $500,000.

Biden’s campaign had previously declined to release a list of his paid speeches, or how much he had earned in total.

The Washington Post found at least 65 instances in which Biden gave a speech or appeared at a book event; in at least 10 instances he did not take a fee, although in some of those cases he was reimbursed for travel expenses.

The campaign financial disclosure forms represented the first detailed look at speeches Biden made after leaving the vice presidency. But because the form stretches back only through part of 2017, there are still several months of speeches whose specific payments remain unknown — although his overall income was listed in his tax returns. The Post found that during that period he delivered about 20 speeches.

Biden appeared to take care to avoid the kind of backlash that 2016 Democratic nominee Hillary Clinton faced in the party primaries for delivering private speeches to Goldman Sachs and other Wall Street interests. Most of Biden’s appearances were in less politically sensitive venues.

With the release on Tuesday, Biden has now made public 21 years of his tax returns, more than any other candidate. President Trump has yet to release any of his tax returns despite an earlier promise to do so.

A review of Biden’s previous tax returns showed the couple’s adjusted gross income at $215,432 in 1998, the first year for which he has made returns available. His income remained in that neighborhood until 2009, when it increased by about $55,000 annually due to Social Security and pension payments.

By Biden’s final years in office, the couple’s gross income totaled about $390,000 annually.

The tax returns showed the Bidens often reported few charitable contributions. For the 10 years preceding 2008, they donated an average of $369 annually to charity — or 0.1 percent of their adjusted gross income. The total increased when Biden served as vice president, with donations of book proceeds to charity, clothing to Goodwill Industries and other contributions.

In recent years, the tax returns show, the charitable contributions saw an uptick.

The Bidens gave $1 million to charity in 2017 — which was 9.1 percent of their taxable income — and $276,000 in 2018, or 6 percent of their income.