New York state investigators have subpoenaed Michael Cohen to testify as part of their investigation into whether Donald Trump and three of his children—Ivanka, Eric and Don Jr.—used the nonprofit Trump Foundation for illegal campaign activity and as a virtual piggy bank for “repeated self-dealing.” The Associated Press reports Cohen’s testimony could help bolster a future criminal case against the foundation or possibly even Trump himself—and could lead New York’s attorney general to request copies of Donald Trump’s tax returns, which Trump has refused to make public. In June, New York Attorney General Barbara Underwood filed a civil suit against the Trump Foundation, saying it used charitable funds to illegally coordinate with Trump’s 2016 presidential campaign, to settle lawsuits against Trump family businesses and even to purchase a $10,000 portrait of Donald Trump hung at one of Trump’s golf resorts.