Senators Claire McCaskill of Missouri and Tom Carper of DE have sent a letter to Defense Secretary Jim Mattis expressing grave concern over Trump's use of his personal smartphone on 9 February.
According to the senators, the vulnerabilities were among the reasons for national security agencies discouraging the use of personal devices.
The Secret Service issued Trump a secured phone for his inauguration, but the president has since reportedly used an unsecured Android phone to tweet from the White House while watching television.
Renowned security professor Matt Blaze described it as "risky as having an email server", referring to Trump's criticism of his presidential contender Hillary Clinton's use of a private email system during her time as secretary of state.
Concerns reached a new high this past weekend when pictures surfaced on social media showing Trump freely discussing state matters regarding North Korea's missile test on the phone while at dinner with Japanese prime minister Shinzo Abe.
"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 in the letter, which was made public Monday.
The senators also questioned whether Trump is properly preserving his activity. As McCaskill and Carper point out, "the National Archives and Records Administration (NARA) 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 device could be vulnerable to hacking if used on unsecured Wi-Fi and cellular networks.
"As you know, hackers often target smartphones in an attempt to obtain sensitive, personal information from the user", wrote senators Tom Carper and Claire McCaskill, noting that these reports about Trump's preference for his old phone are quite troubling.
Finally, they want to know if DISA consulted with NARA "to ensure that all security measures allow for the preservation of any presidential records created through President Trump's use of the device".
The senators asked Mattis to respond by March 9.