The report notes that officials within the White House moved all official records of the call from a standard electronic document storage system to one intended to store only the most classified U.S. national security secrets.

This system is used for the highest-level of classified intelligence, a level beyond "top secret" that is accessible only on a need-to-know basis to specific members of the NSC and intelligence community. And that fact has raised questions as to why the Trump administration would use such a highly-secure, secretive server to store what Trump has called an entirely appropriate conversation.

Specifically, the transcript was placed into a computer system managed directly by the National Security Council (NSC) Directorate for Intelligence Programs, which is reserved for so-called "codeword-level" intelligence. Motherboard spoke to four former members of the NSC for previous presidential administrations to learn more about what the system is, what it's used for, and who can access it. Each of them was shocked that the Trump administration used the codeword system for a presidential phone call.

"What was the nature of that sensitivity? The clear implication is that the White House understood that the president's remarks could be legally and politically problematic," he said. "There was no other classified 'factual' material in the transcript that would justify a move to a more secure server."

Steven Aftergood, director of the Project Government Secrecy at the Federation of American Scientists, told Motherboard that putting these records on this system "signifies an awareness in the White House that this was not a 'normal' conversation."

"The transcript [of the call] was loaded into a separate electronic system that is otherwise used to store and handle classified information of an especially sensitive nature," the complaint notes.

Motherboard spoke to four former members of the NSC who had direct knowledge of the system in question under previous presidential administrations. Three of them—two of whom were granted anonymity to discuss the specifics of highly sensitive and potentially classified filing systems—said that they are unaware of even a single instance in which details of a presidential call with a foreign head of state was stored in the codeword-level system.

"You don't have hundreds of people getting access to presidential calls. They're tightly controlled, so, it's not as if this would have been floating around with lots of people getting access to the first place. To take the added step of telling the White House lawyers to put this on that system is beyond bizarre to me," Kelly Magsamen, vice president of national security and international policy at thinktank Center for American Progress, and who served in the NSC for two presidents, told Motherboard. "It suggests they know it was extremely damaging."

To be clear, the existence of this sensitive server in and of itself is not unusual. The sensitive server is typically used to store details on covert action and other highly sensitive information with a high degree of access limitation. But multiple experts who have used the system in previous presidential administrations said that it's troubling for the administration to use a highly-classified server to store embarrassing information.

From there, the director who handles the transcript and other notes creates a "packet number" that can be used to track it in the future (notes are required to be saved as part of the Presidential Records Act ). The director who prepares the packet decides what parts of it should be classified, according to two former NSC members. There are four general systems where it can go, they said. Each of these must be accessed using a different computer:

"Basically the situation room would route the call from wherever, like the outgoing number to let's say the country is Ukraine, through the Sit Room, up to the Oval or wherever the president was to take it," Tommy Vietor, who worked on the NSC under President Obama, explained on the podcast Pod Save the World. "So the Sit Room could listen to the call or type out a transcript."

"Basically, unless the conversation is about codeword-level stuff, it wouldn't be generated and transmitted on that system," Nate Jones, the founder of Culper Partners and the former director of counterterrorism at the NSC told Motherboard. "It's cumbersome not just to get things on there, but nobody can look at it and access it without going through a very involved process. You are effectively limiting people's ability to disseminate that information."

Jones said it is impossible to access the codeword-level system outside of the White House, and that any "president wouldn't have the first idea of how to get into it."

"He has the right to manage people to do things with it within reason, but he wouldn't on his own accord have the ability to even get into the room it's located on his own. He'd need help," he said. "The same is true of the National Security Advisor and people like that, but they could direct people who have access to it to provide them information. Once it's in the system, they have maximum control over who sees it."

Jones added that because of the compartmentalization, it could be classified in such a way so that essentially no one had access to it.