Previous calls between President Trump and leaders of Russia and Saudi Arabia were placed in the same highly-classified system as Mr. Trump's controversial call with Ukrainian President Volodymyr Zelensky, a former senior administration official with knowledge of the system told CBS News.

National Security Council officials took other measures to keep calls within smaller circles. A former White House official told CBS News that restrictions on presidential call "transcripts" go back to the early days of the administration. It is not standard practice to move call records to the more secure server, but it has happened on a number of occasions during Mr. Trump's time in office. There is a practice of cleaning up after these calls to protect the president, the source told CBS News.

CNN and The New York Times first reported the White House's efforts to conceal other calls between Mr. Trump and foreign leaders.

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Following the leaks of two previous calls early in the administration with leaders of both Mexico and Australia, the White House took precautions to protect these calls from a wider audience, according to the former senior administration official.

Concerns about Mr. Trump's calls with foreign leaders have emerged as the evolving story of an anonymous whistleblower and Mr. Trump's call with Volodymyr saw two major developments on Thursday: the release of the whistleblower's complaint at the center of the House impeachment inquiry, and the public testimony of Joseph Maguire, the acting director of national intelligence, who delayed providing it to Congress.

In the days following Mr. Trump's July 25 conversation with Zelensky, the White House moved to restrict access to records of the call, according to the anonymous whistleblower complaint.

The whistleblower concluded from these actions "that White House officials understood the gravity of what had transpired in the call." And then, White House lawyers "'directed'" officials "to remove the electronic transcript from the computer system in which such transcripts are typically stored for coordination, finalization, and distribution to Cabinet-level officials."

At first, the whistleblower said, the call was expected to be "routine," but afterward, there was a sense from some in the White House that the president had abused his power. White House officials who gave the whistleblower information said they "were deeply disturbed by what had transpired in the phone call."

Internally, some officials saw this as an "abuse of the system" and felt it was "not consistent with the responsibilities of the Directorate for Intelligence Programs," the complaint said.

White House officials also, according to the complaint, told the whistleblower it wasn't the first time during the Trump administration "that a Presidential transcript was placed into this codeword-level system solely for the purpose of protecting politically sensitive rather than national security-sensitive information."