The massive data leak known as the Panama Papers has revealed the law firm Mossack Fonseca set up more than 1,000 shell companies inside the United States, once again raising questions about the United States’ role as an offshore tax haven. The papers show more than 600 shell companies were set up in Nevada alone. Matthew Gardner of the Institute on Taxation and Economic Policy said, “We should be thinking about this as a very American problem, and a problem that arguably is worse here in the states than it is in Panama.”