"Public reports originally indicated that President Trump began using a 'secure, encrypted device approved by the U.S. Secret Service' prior to taking office," the Senators wrote. "Subsequent reports, however, suggest that President Trump may still be using his personal smartphone, an 'old, unsecured Android phone.' While it is important for the President to have the ability to communicate electronically, it is equally important that he does so in a manner that is secure and that ensures the preservation of presidential records."
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Sens. McCaskill and Carper describe these news reports as "troubling," since hackers can target unsecured devices and activate a phone's audio recording, camera, and location tracking. Even when people take precautions to secure their devices, hackers continue to exploit security weaknesses or create new pathways to personal data, the Senators said.
"These vulnerabilities are among the reasons why national security agencies discourage the use of personal devices," the letter reads. "The national security risks of compromising a smartphone used by a senior government official, such as the President of the United States, are considerable."
Sens. McCaskill and Carper asked Secretary Mattis to confirm whether the president has a "secured, encrypted smartphone for his personal use." They also asked to review the Defense Department's written policies for securing President Trump's personal device.
Alongside the security risks, the Senators are also concerned that presidential records — including Trump's tweets — may not be properly recorded if they are created on his personal device. "The National Archives and Records
Administration considers President Trump's tweets to be records that must be adequately documented, preserved, and maintained for historic purposes, as required by the Presidential Records Act," the letter explains.
One of the questions posed to Secretary Mattis was whether the Defense Department collaborated with the National Archives and Records Administration to ensure that the security measures on Trump's phone don't interfere with the preservation of presidential records.
The Senators asked Secretary Mattis to respond by March 9th.
Last month, McCaskill and Carper wrote a letter to White House Counsel Donald McGahn seeking to find out if Trump's staff complied with federal law regarding the use of private email accounts to conduct official business. They asked that he respond by February 10th. A spokesperson for Sen. McCaskill told BuzzFeed News that they have not received a response.