(Bloomberg) -- Democratic front-runner Joe Biden is building his presidential campaign around the middle class values he shares with his core voters. Now he may need to convince them he’s still one of them.New financial disclosures show that Biden has become a multimillionaire in the two years since he left the Obama administration. The former vice president and his wife, Jill, earned more than $15.6 million in 2017 and 2018, according to tax returns for those years released by his campaign on Tuesday.Their net worth is between $2.2 million and $8 million, according to a separate financial disclosure filed Tuesday that doesn’t include their real estate holdings. By contrast, Biden’s disclosure with the federal Office of Government Ethics for 2016, his last year at the White House, showed the couple’s assets were worth between $303,000 and $1 million and they had liabilities between $560,000 and $1.2 million.Biden’s change in fortunes could provide rich fodder for his rivals for the Democratic nomination, many of whom are already trying to portray the 76-year-old as an out-of-touch member of the Washington elite. The wealth is also likely to open up a new line of attack by Republicans and President Donald Trump, eager to tear down his reputation as “middle class Joe.”The bulk of the Bidens’ new income came from payments for the memoirs they’ve each written, as well as speaking engagements.Speaking EngagementsBiden also filed a disclosure form with the Federal Election Commission that details 47 paid speaking engagements in 2017 through early 2019 for which he was paid as much as $181,000 each. Most speaking fees were paid by universities and theaters or entertainment companies such as Live Nation Worldwide Inc. and CAA Premium Experience.Hillary Clinton, the former Obama secretary of state and 2016 Democratic nominee, faced attacks throughout her campaign for speaking behind closed doors to banks and other financial services companies. Biden did not do any corporate speaking engagements, and his campaign said that all speeches were open to the public and that more than half were also open to press coverage.The Bidens donated $275,796 -- about 6% -- of their more than $4.5 million in income in 2018, according to their tax returns. A year earlier, when the Bidens reported more than $11 million in income, they donated more than $1 million, more than 9% of their total earnings.The Bidens paid $3.7 million in federal income taxes in 2017 and $1.5 million in 2018. Their state and local taxes totaled $736,613 in 2017 and $344,944 in 2018.Joe Biden’s income in 2017 and 2018 also included about $400,000 annually from the University of Pennsylvania for his role as Benjamin Franklin Presidential Practice Professor. Jill Biden took in slightly more than $90,000 each year for her professorship at Northern Virginia Community College.In addition to a long-held home in the Wilmington, Delaware, area, the Bidens bought a house in Rehoboth Beach for $2.7 million in 2017.\--With assistance from Laura Davison and Bill Allison.To contact the reporter on this story: Jennifer Epstein in Washington at jepstein32@bloomberg.netTo contact the editors responsible for this story: Alex Wayne at awayne3@bloomberg.net, Max Berley, Laurie AsséoFor more articles like this, please visit us at bloomberg.com©2019 Bloomberg L.P.