Angst is growing among Senate Republicans over the rise of White House aide Stephen Miller after Kirstjen Nielsen's ouster as Homeland Security secretary last week.

Nielsen's departure and other high-level purges directed by the White House — reportedly spearheaded by Miller — have battered the department's leadership and underscored tensions between the Senate and the White House. Some GOP senators, who have been vocal about their support for Nielsen, are worried the shakeup will lead to an unstable and highly politicized department.

Miller, 33, has made a name for himself acting as a fierce public surrogate for President Trump and pushing for a harder line on immigration. He served as communications director for then-Sen. Jeff Sessions from 2012 to 2016 before joining the Trump campaign in January 2016.

[ Related: Trump says he is not 'cleaning house' even as more Homeland Security departures expected]

“I hope that he’s got more voices than that one in his ear on these issues, because, yeah, I think it’s important that he get a whole perspective and range of opinions,” Senate Majority Whip John Thune, the second-highest ranking Republican in the Senate, said of Miller.

When the South Dakota senator was asked by the Hill who else Trump should be listening to, he chuckled and replied, "Some of them are now gone."

Texas Sen. John Cornyn, who previously served as Senate majority whip, echoed the worry that the purges at Homeland Security are destabilizing the department.

“I think what we need is a consistent message because I think there are some voices in the White House who are working counter to that message and particularly creating more problems for the administration by losing senior leadership,” Cornyn said when asked about Miller.

“Churn is not helpful to [Trump] or to DHS,” Cornyn added. “It creates more churning and it takes more oxygen out of the environment.”

Miller has reportedly recommended Trump dump two other high-level Homeland Security staffers, Lee Cissna, head of U.S. Citizenship and Immigration Services, and Kathy Nuebel Kovarik, who is head of policy and strategy under Cissna.

Both worked as Senate staffers under Senate Finance Committee Chairman Chuck Grassley, and Miller's push for their dismissal has put the senior Iowa senator at odds with the administration.

“I know Cissna well. I know Kathy Kovarik well. They’re qualified people. They are good for the president. I heard that they were going to be dismissed and that irritates me," Grassley, R-Iowa, said.

“I don’t know whether he’s been an effective adviser for the president,” he added of Miller.

After Nielsen's resignation, Trump announced via Twitter that Customs and Border Patrol Director Kevin McAleenan would be named acting secretary. The legality of the move, however, was questioned after House Homeland Security Committee members pointed out that by law the next in line was Under Secretary for Management Claire Grady, a figure wildly unpopular with Trump.

Trump asked for Grady's resignation on Tuesday, allowing McAleenan to become the acting secretary when Nielsen's resignation took effect Wednesday.