“Those documents are usually only available to law enforcement, and while the White House has the authority to request the documents, they typically don’t – largely because the Department of Justice is supposed to be insulated from political pressure to take on, or complete, an investigation.”
The Chief Executive IS the head of law enforcement. He is OVER the Attorney General. It’s the same way he is the commander in chief of the military. The FBI has zero right to withhold any work product from him.
It would be impeachable for a president to use the DOJ to go after someone for personal or political reasons (for example the way Obama did with IRS and FISA courts)
But yes, a president may examine any work product of the executive branch.
He may walk in and open any file cabinet he pleases at the Justice dept or at the CIA. He may land at Area 51 and go anywhere he pleases.
He cannot so much as set the speed limit on a city street. He does not have power over citizens like that. He cannot walk into the Congress, or the Supreme Court and open a drawer. But yes, he is fully head of the executive branch, and that’s how it is kiddies. Nobody in that branch can tell him something is above his pay grade.
But the FISA court isn't part of the Executive.