"Perhaps the need for a special lawyer would not be so clear and urgent if Clinton does not have the disturbing track record of this matter," he wrote.
In May 2017, Mr. Whitaker wrote an op-ed for The Hill in which he praised Mr. Trump's decision, James B. Comey, F.B.I. Director. He said he did not agree with Mr. Comey's assessment that "no sensible prosecutor" would initiate criminal proceedings against Ms. Clinton.
It is not clear whether the President intends to appoint Mr Whitaker as the next Attorney General, or whether he will choose someone of greater size and experience. But Mr. Whitaker is assisted by Senator Charles E. Grassley, the Iowa Republican, who chairs the Senate Judiciary Committee. Mr. Grassley assisted Mr. Whitaker in his appointment as a US Attorney in Iowa in 2004, and was pleased with the decision on Wednesday to appoint him Deputy Prosecutor General.
"I look forward to working with Matt Whitaker as he takes over the administration of the Department of Justice," Grassley said in a statement. "As Iowan, whom I've known for many years, Matt will work hard and make us proud. The Ministry of Justice is in good hands during this transitional period. "
It is likely that Mr. Whitaker will be in position until at least early next year because the Senate's calendar would make it nearly impossible to confirm a new Attorney-General before the end of the current term in December.
Mr Whitaker's rise comes after a New York Times article revealed in September that Rosenstein had secretly talked about his talks with the president and talked about how he wanted to remove Mr Trump from office with the 25th amendment.
After the report, Mr. Rosenstein offered his resignation, and Mr. Whitaker was expected as deputy attorney general because the White House advisors had told him it would happen.
On Wednesday, Mr Trump handed over to Mr Rosenstein, his confirmed Deputy Prosecutor General, for Mr Whitaker, a member of the division.