Sen. Chuck Grassley, R-Iowa, is demanding answers following Defense Secretary Ash Carter’s admission of using a private email account, which came to light last year.

“It is troubling to learn of your use of personal email for official matters, especially since you continued using that arrangement even after the risks of private use were made clear when news of [Secretary of State Hillary] Clinton’s use broke in March 2015,” Grassley wrote in a letter to Carter Monday.”