Sen. Tom Carper, D-Delaware, recently sent a letter to Department of Defense Secretary Mattis about serious security concerns related to President Donald Trump’s reported use of a personal, unofficial smartphone.

“Public reports originally indicated that President Trump began using a ‘secure, encrypted device approved by the U.S. Secret Service’ prior to taking office. Subsequent reports, however, suggest that President Trump may still be using his personal smartphone, an ‘old, unsecured Android phone,’” Carper wrote in a joint letter with Sen. Claire McCaskill, D-Missouri. “The national security risks of compromising a smartphone used by a senior government official, such as the president of the United States, are considerable. In addition to these security risks, media reports suggest that President Trump often uses his personal Android phone to communicate via his personal Twitter account.”

“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,” the senators continued. “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 senators asked the Department of Defense to provide information regarding its efforts to oversee, develop and implement protective measures for President Trump’s use of a personal smartphone no later than March 9.