Hillary Clinton arrives to sign her book "Hards Choices" at a bookstore on Martha's Vineyard on August 13, 2014. According to the Clintons' 2015 tax returns, the couple earned $3.1 million from book advances and royalties. Nicholas Kamm/AFP/Getty Images hide caption

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Washington, D.C., Mayor Muriel Bowser last month. Larry French/Getty Images hide caption

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D.C. PAC Shutters, Highlighting Fine Ethical Line For Groups Across The Country

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Democratic mayoral candidate Jim Kenney benefited from a super PAC that helped him win in the city's Democratic primary election. Matt Slocum/AP hide caption

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Coming To A Mayor's Race Near You: SuperPACs Moving Into Cities

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A volunteer with the Koch-funded Libre Initiative directs people in 2014 as groceries are distributed at a food bank it partially sponsors in San Antonio. Eric Gay/AP hide caption

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Rick Perry ended his presidential campaign Sept. 11, but there was $13 million left in the bank of a superPAC supporting him. The superPAC says it's given donors their money back. Scott Olson/Getty Images hide caption

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'Social Welfare' Organizations Play Big Role In Presidential Politics

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Alex Brandon/AP

Why Does The Mortgage-Interest Tax Deduction Still Exist?

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Some superPAC donors are hiding from public scrutiny. iStockphoto.com hide caption

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On The Million-Dollar Trail Of A Mystery SuperPAC Donor

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Charles Dharapak/AP

When Lobbyists Pay To Meet With Congressmen

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