DHS Secretary Kirstjen Nielsen’s resignation Sunday provides a window into White House senior adviser Stephen Miller’s campaign to replace more moderate voices — like Nielsen — with immigration hardliners at the Departments of Homeland Security, Justice and State.

According to a Sunday Politico report, while it is unclear how much direct influence Miller had over Nielsen’s ouster, he has been contacting lower-level officials and threatening them to staunch the flow of immigrants across the border, or else.

In one example, Miller reportedly had a hand in the abrupt pulling of ICE chief candidate Ronald Vitiello’s nomination Friday after Vitiello expressed ambivalence about closing down the U.S.-Mexico border.

“There’s definitely a larger shakeup abreast being led by Stephen Miller and the staunch right wing within the administration,” a person close to Nielsen told Politico. “They failed with the courts and with Congress and now they’re eating their own.”