I’d bet it was either John Kerry or one of his top aides.

Via TWS:

The belief that the prime minister of Israel is “chickenshit” is “not the administration’s view,” a spokesperson for the National Security Council says in a statement. Jeffrey Goldberg of the Atlantic reported Tuesday that a “senior administration official” viewed Benjamin Netanyahu, the prime minister of Israel, as the most frustrating foreign leader to the White House and the State Department. […]

The belief that the prime minister of Israel is “chickenshit” is “not the administration’s view,” a spokesperson for the National Security Council says in a statement. Jeffrey Goldberg of the Atlantic reported Tuesday that a “senior administration official” viewed Benjamin Netanyahu, the prime minister of Israel, as the most frustrating foreign leader to the White House and the State Department.