There's precedent for White House Signal chat leak and it's more than 100 years old 

The Trump administration is investigating how the Goldberg error happened, as well it should. It seems unlikely that anyone will be punished too severely for this unintentional breach.

Tevi Troy is a senior fellow at the Ronald Reagan Institute and a former senior White House aide. He is the author of five books on the presidency, including "The Power and the Money: The Epic Clashes Between Commanders in Chief and Titans of Industry." 

Of course, Graham’s paper would subsequently be involved in some much more significant leaks. One of them was the Pentagon Papers during the Richard Nixon administration. In this case, RAND Corporation official and Vietnam War skeptic Daniel Ellsberg leaked documents about the U.S. national security establishment’s thinking on Vietnam during the Kennedy and Johnson administrations.