Sen. Chuck Grassley, R-Iowa, said Monday he was concerned about reports of more imminent departures in the White House after the latest shakeup of top immigration positions.

During a Monday night interview on Fox News, Grassley said he was caught off guard by Homeland Security Secretary Kirstjen Nielsen submitting her resignation but understood that President Trump has the prerogative to decide who he wants to run the department.

“I am very surprised. But the president has a right to have whoever he wants,” Grassley said. “And the acting person is very well qualified.”

Trump announced Nielsen’s departure over Twitter Sunday after a heated meeting on the border and immigration. But Grassley said he is more concerned about reports that others could be on the cutting board, according to the Washington Post.

L. Francis Cissna, the head of Citizenship and Immigration Services, and John Mitnick, a senior member of Nielsen’s team, might be pushed out next, and Grassley said this makes him “very, very concerned.”

“One, those are good public servants,” he said. “Secondly, besides the personal connection I have with them and the qualifications they have, they are the intellectual basis for what the president wants to accomplish in immigration.”

When Grassley served as chairman of the Senate Judiciary Committee, Cissna and he worked closely together.

“The president has to have some stability and particularly with the number one issue that he’s made for his campaign, throughout his two and a half years of presidency,” Grassley said, noting he has been in contact with Trump’s acting chief of staff, Mick Mulvaney, about the issue Monday.

The senior senator from Iowa also knocked Stephen Miller, one of Trump’s senior policy advisers and an immigration hardliner who reportedly played a big role in orchestrating Nielsen's ouster.

“I think it would be hard for him to demonstrate he’s accomplished anything for the president,” Grassley said.

This shakeup also includes the coming departure of Secret Service Director Randolph “Tex” Alles, who Trump reportedly called “Dumbo” behind his back. James Murray was named as Alles’ replacement and Nielsen is set to be replaced by Kevin McAleenan.

The departures come days after the nomination of Ron Vitiello, who was to lead Immigration and Customs Enforcement, was suddenly pulled from consideration.