Special counsel Robert Mueller has impaneled a federal grand jury in Washington, D.C., as he expands a probe into Russia’s alleged interference in the 2016 presidential election. The move, first reported by The Wall Street Journal, gives Mueller’s investigation the power of subpoena and opens the door to possible criminal charges against President Trump and his associates. Mueller is reportedly looking into whether Trump’s firing of FBI Director James Comey last May constituted obstruction of justice. Mueller has also reportedly subpoenaed documents related to the business dealings of former Trump campaign chair Paul Manafort, as well as General Michael Flynn, Trump’s one-time national security adviser. News of the grand jury came after Mueller added a 16th lawyer to his team of investigators: Greg Andres, a former member of the Justice Department’s Criminal Division and white-collar lawyer specializing in foreign bribery.