Attorney General William Barr is a well-known subscriber to the unitary executive theory, which postulates that the president is granted broad powers under the Constitution and that there are relatively few mechanisms to pursue oversight of the White House, The Hill reported:

The attorney general has argued in the past that Congress cannot make a law against the president exercising executive powers for corrupt purposes and that presidents have authority over investigations even when those probes are focused on their activity…

Barr’s forceful defense of Trump comes as some of the president’s allies grumble that he has failed to publicly back the White house during the impeachment investigation, particularly after a report surfaced that Barr turned down a request from Trump to hold a press conference saying no wrongdoing occurred in the president’s dealings with Ukraine, the focus of the House’s impeachment investigation. 

Read the Attorney’s defense of Trump in this really interesting article by the Hill.