In the past few years, with Hezbollah acting as a shield, Iran has inched closer to acquiring a nuclear weapon.

According to a recent report by the U.S. Director of National Intelligence, the regime in Tehran had recently begun to undertake "activities that better position it to produce a nuclear device, if it chooses to do so." Most American experts believe that Iran has enriched enough uranium to about sixty-per-cent purity to build about three nuclear weapons.

If the Iranians were to decide to deploy a nuclear weapon, they would need to enrich that uranium to ninety-per-cent purity—a process that could be done in a matter of weeks. Then the regime would have to build a trigger for the device. Some U.S. experts maintain that the Iranians do not yet have that capability, but others think that they are, at least, much closer to it than they were.

In a report published in August, David Albright and Sarah Burkhard, of the Institute for Science and International Security, wrote that Tehran appeared to have shortened the time it needed to achieve "breakout"—acquiring a bomb—to less than six months.

"Iran can make a crude nuclear weapon far faster than commonly assessed," they wrote. That brings us back to Hezbollah: if the Iranian insurance policy in Lebanon has been diminished, Khamenei could decide that the time has come to deploy a nuclear weapon. This could give him a sense of security that recent events have stripped away. "The simplest thing for Khamenei to do is build a bomb," Gerecht, the former C.I.A. officer, said.

Few of the American and Israeli officials I have spoken with believe that Israel, acting alone, could destroy Iran's nuclear infrastructure, especially the underground nuclear-enrichment site at Fordow, south of Tehran. The only air force capable of destroying that reactor is that of the United States.

Like Presidents Donald Trump and Barack Obama before him, Biden has never ruled out using military force to stop the Iranian regime from acquiring a nuclear weapon, but he has shown little willingness to contemplate such a momentous action. On Wednesday, Biden said that he would not support an Israeli attack against Iran's nuclear facilities.

That does not mean the Israelis wouldn't attempt one, and a strike that only partially succeeded could put enormous pressure on the United States to finish the job. Israel's success against Hezbollah could encourage the Israelis to undertake more aggressive action against the Iranian regime, including encouraging dissent within the country or even attacking it directly.

What might such a campaign look like? Possibly strikes against Iran's leaders, or its oil-export facilities, or its military bases. In a three-minute video addressed to the Iranian people, released on Monday, Netanyahu suggested that such activities may be about to begin. "When Iran is finally free—and that moment will come a lot sooner than people think—everything will be different," he said.