The Kremlin might know more about conversations between President  Trump, Rudy Giuliani and others involved in the Ukraine gambit that led to Congress’ impeachment inquiry than congressional investigators themselves. The reason for this alarming reality? A dangerous fondness for cellphones.

Trump’s insistence on using his personal cellphone for official communications was a problem the moment he stepped into the Oval Office – after a campaign spent railing against rival Hillary Clinton for sending state emails on a private server. Now, call records obtained by the House have resurrected concerns about how the president and his closest associates communicate about the most sensitive of matters, and who exactly might be listening.

Trump claims he relies exclusively on government-issued devices hardened against hacks. But last year, The New York Times reported he favored a mass-market iPhone for dialing his friends, and Chinese spies often eavesdropped for insights on how they might sway the administration. Even if all the commander in chief’s phones are now specifically programmed for protection, there’s still a risk if they’re not routinely scrubbed or swapped out – measures Trump in the past allegedly declared “too inconvenient.”

Security experts also say cellphones are generally more vulnerable than landlines. Adversaries eager to intercept privileged chats, for example, can “spoof” the towers through which calls are routed. John Kelly’s success in getting Trump to move to White House channels was short-lived; the president discovered that meant the then-chief of staff could access a log of his calls, and he reverted to his old habits.

Even if Trump conducted conversations only from sanctified facilities such as the Situation Room, they would still be only as safe from surveillance as their recipient – which, as witness testimony these past few weeks has revealed, is not safe at all. Giuliani’s communications, it seems, were not encrypted with any of the widely available services such as WhatsApp and Signal. Similarly, U.S. ambassadors speaking to the president are supposed to do so from an embassy on a secure line, not from a restaurant in Kiev on an unsecured cellphone.

The White House, in short, seems content to privilege convenience over secrecy. Barack Obama famously fought to keep his i-Phone when he became president. He won, but the device he ended up with was so restricted for security’s sake that using it, he said, was “no fun.” At least he understood that it wasn’t supposed to be.