Adam Davidson writes that a Senate panel’s request for information from a Treasury enforcement unit suggests a broader scope to its investigation. The FinCEN request is particularly interesting because the unit enforces money-laundering laws and is familiar with Donald Trump’s holdings, specifically the Taj Mahal casino, in Atlantic City. Trump opened the Taj Mahal in 1990. He sold half of his shares in 2004, as part of a bankruptcy settlement, but remained a minority owner. In 2015, the Taj Mahal admitted to “willfully” violating the law by letting many suspicious transactions go unreported to the authorities, and agreed to pay a ten-million-dollar fine—one of the largest ever for a casino.