The crucial factor today is that Iran has the knowledge needed to fashion a nuclear device, but it lacks the material—highly enriched uranium or plutonium—necessary to build nuclear bombs, Daryl Kimball, the executive director of the Arms Control Association, in Washington, D.C., told me. “Whatever role Mr. Fakhrizadeh has played in the Iranian nuclear program, his assassination will not have material effect on Iran’s capability to amass more enriched uranium,” Kimball said. The enrichment program falls under the Atomic Energy Organization of Iran, which is headed by Ali Akbar Salehi, an M.I.T. graduate. Salehi was a key player during the two years of intense international diplomacy that led to the Iran nuclear deal, in 2015. He and his organization were sanctioned by the Trump Administration, in January. “But since Iran now has the know-how, no single Iranian scientist is essential to assembling that technology into a bomb,” Tabatabai said. Instead, that decision would be political, and would be made by the Supreme National Security Council, then submitted to Supreme Leader Ayatollah Ali Khamenei for his final approval. This is the same decision-making process that was involved in agreeing to talks with the United States in 2013, and to the eventual nuclear deal.

The domestic fallout from Fakhrizadeh’s assassination could be more impactful than the operation itself, partly because of the humiliation. The regime faces pressure to respond with bigger and bolder military action than it has in the past. “This is a truly serious blow to Iran, primarily in the eyes of the Iranian public,” a leader of a Middle Eastern country, who asked not to be named, told me. “This has very profound implications to its internal dynamics. Therefore, they may choose to retaliate to overcome the sense of embarrassment and vulnerability.” Kayhan, a hard-line paper close to the Supreme Leader, urged the government to attack Haifa, the Israeli port city, as a “deterrence, because the United States and the Israeli regime and its agents are by no means ready to take part in a war and a military confrontation.”