In the photos, Waltz has apparently remembered to turn his papers face down before the troupe of reporters — print, TV, photo, radio – entered the crowded Cabinet Room of the White House. But he’s holding his phone, with the messaging app open, in a way that is easy to spot.

A photo taken this week showed Mike Waltz using an app that looks like—but is not—Signal to communicate with top officials. "I don't even know where to start with this," says one expert.