The Trump administration’s error in adding a journalist to a top secret Signal group chat about attack plans against Houthi terrorists in Yemen has thrown several officials into hot water.

The Atlantic‘s editor-in-chief, Jeffrey Goldberg, reported Monday that he was unexpectedly added to a Signal group chat earlier this month, where top Trump administration officials discussed plans to attack Houthi targets. The report sparked sharp reactions over the apparent security lapse, including calls for some of the officials in the chat to resign. Here is what to know about the controversy.