While it is an obvious attempt at shutting down the Russia investigation by appointing someone with a clear bias towards Trump constitutional lawyers including Kellyanne Conway's husband argue it is also unconstitutional.
"But Professor Calabresi and Mr. Trump were right about the core principle. A principal officer must be confirmed by the Senate. And that has a very significant consequence today.
It means that Mr. Trump’s installation of Matthew Whitaker as acting attorney general of the United States after forcing the resignation of Jeff Sessions is unconstitutional. It’s illegal. And it means that anything Mr. Whitaker does, or tries to do, in that position is invalid.
Much of the commentary about Mr. Whitaker’s appointment has focused on all sorts of technical points about the Vacancies Reform Act and Justice Department succession statutes. But the flaw in the appointment of Mr. Whitaker, who was Mr. Sessions’s chief of staff at the Justice Department, runs much deeper. It defies one of the explicit checks and balances set out in the Constitution, a provision designed to protect us all against the centralization of government power."
Because Mr. Whitaker has not undergone the process of Senate confirmation, there has been no mechanism for scrutinizing whether he has the character and ability to evenhandedly enforce the law in a position of such grave responsibility. The public is entitled to that assurance, especially since Mr. Whitaker’s only supervisor is Mr. Trump himself, and the president is hopelessly compromised by the Mueller investigation. That is why adherence to the requirements of the Appointments Clause is so important here, and always."
https://www.nytimes.com/2018/11/08/opinion/trump-attorney-general-sessions-unconstitutional.html
"But Professor Calabresi and Mr. Trump were right about the core principle. A principal officer must be confirmed by the Senate. And that has a very significant consequence today.
It means that Mr. Trump’s installation of Matthew Whitaker as acting attorney general of the United States after forcing the resignation of Jeff Sessions is unconstitutional. It’s illegal. And it means that anything Mr. Whitaker does, or tries to do, in that position is invalid.
Much of the commentary about Mr. Whitaker’s appointment has focused on all sorts of technical points about the Vacancies Reform Act and Justice Department succession statutes. But the flaw in the appointment of Mr. Whitaker, who was Mr. Sessions’s chief of staff at the Justice Department, runs much deeper. It defies one of the explicit checks and balances set out in the Constitution, a provision designed to protect us all against the centralization of government power."
Because Mr. Whitaker has not undergone the process of Senate confirmation, there has been no mechanism for scrutinizing whether he has the character and ability to evenhandedly enforce the law in a position of such grave responsibility. The public is entitled to that assurance, especially since Mr. Whitaker’s only supervisor is Mr. Trump himself, and the president is hopelessly compromised by the Mueller investigation. That is why adherence to the requirements of the Appointments Clause is so important here, and always."
https://www.nytimes.com/2018/11/08/opinion/trump-attorney-general-sessions-unconstitutional.html