A Democratic senator has asked newly confirmed Homeland Security Secretary Markwayne Mullin to explain the department’s racist social media presence and assure the agency has not been “infiltrated by violent extremists.”

Sen. Sheldon Whitehouse, D-R.I., pointed to a March bulletin from Colorado law enforcement analysts that was unearthed by The Intercept last month. It warned that DHS posts using language popular with neo-Nazis could inspire acts of far-right violence within the U.S. as well as prompt white supremacists to join the agency.