Two congressional Democrats have sent a formal letter to top White House and law enforcement officials, seeking more information about the president’s use of an unsecured cell phone.

The letter, which was sent Wednesday by Rep. Ted Lieu (D-California) and Rep. Ruben Gallego (D-Arizona), comes after recent media reports that Donald Trump is making "increased use" of his personal phone.

Last year, Trump reportedly had an iPhone with just one app on it: Twitter.

"While cybersecurity is a universal concern, the President of the United States stands alone as the single-most valuable intelligence target on the planet," the congressmen write.

"Given the apparent lack of progress the Administration has made since initial reports in 2016 of the President’s poor operational security, it appears the only thing standing between the Office of the President and the next national security nightmare is a combination of President Trump’s personal restraint and sheer luck. Our national security should not depend on whether the President clicks on a malicious link on Twitter or his text application, or the fortuity of foreign agencies not knowing his personal cell number."

The letter goes onto ask a number of questions of the White House Communications Agency, the entity responsible for the president’s infosec needs.

How frequently does the WHCA update the President’s phone’s operating system? Does the President use encryption when he makes phone calls or texts from his personal cell phone? How has WHCA adapted to the growing threat of "Stingray" devices, or IMSI catchers, in Washington D.C., especially given the President’s alleged proclivity for making outgoing voice calls on his personal cell phone?

There are also a list of questions specifically for the Secret Service and for the Office of the Director of National Intelligence.

Neither the WHCA, the Secret Service, nor the ODNI immediately responded to Ars’ request for comment.