WASHINGTON—Longstanding U.S. worries about the threat that Iran and its agents pose on U.S. soil intensified in the hours after the 2020 assassination of a prominent Iranian military commander, when the Department of Homeland Security bolstered security at thousands of federal buildings against the possibility of retaliation, according to current and former senior U.S. officials.
That effort, code-named Operation Resilience according to one of the officials, was premised in large part on the concern that Iran would use its proxy Hezbollah to attack the U.S. homeland in response to the killing in a U.S. airstrike in Baghdad. The slain commander, Maj. Gen. Qassem Soleimani, headed Iran’s Quds Force, an elite unit responsible for Iran’s shadow wars and military expansion.