Shapiro served as Deputy Assistant Secretary of Defense for the Middle East until January—charged with, among other things, considering scenarios in which tensions between Israel and Iran escalated into all-out war and preparing U.

Oman and Qatar were leading efforts to begin ceasefire talks, while mediators said Iran was open to resuming nuclear negotiations if Israel’s attacks stop.

Iran has vowed to retaliate against the U.S., too, while Trump has warned: “If we are attacked in any way, shape, or form by Iran, the full strength and might of the U.S. Armed Forces will come down on you at levels never seen before.” Here’s what to know about U.S. involvement so far.