Meir Dagan, while not taking credit for the assassinations, has praised the hits against Iranian scientists attributed to the Mossad, saying that beyond “the removal of important brains” from the project, the killings have brought about what is referred to in the Mossad as white defection — in other words, the Iranian scientists are so frightened that many have requested to be transferred to civilian projects. “There is no doubt,” a former top Mossad official told me over breakfast on Jan. 11, just a few hours after news of Ahmadi-Roshan’s assassination came from Tehran, “that being a scientist in a prestigious nuclear project that is generously financed by the state carries with it advantages like status, advancement, research budgets and fat salaries. On the other hand, when a scientist — one who is not a trained soldier or used to facing life-threatening situations, who has a wife and children — watches his colleagues being bumped off one after the other, he definitely begins to fear that the day will come when a man on a motorbike knocks on his car window.”

As we spoke, a man approached and, having recognized me as a journalist who reports on these issues, apologized before asking: “When is the war going to break out? When will the Iranians bomb us?” The Mossad official smiled as I tried to reassure the man that we wouldn’t be nuked tomorrow. Similar scenes occur almost every day — Israelis watch the news, have heard that bomb shelters are being prepared, know that Israel test-fired a missile into the sea two months ago — and a kind of panic has begun to overtake Israeli society, anxiety that missiles will start raining down soon.

Dagan believes that his five-fronts strategy has succeeded in significantly delaying Iran’s progress toward developing nuclear weapons; specifically “the use of all the weapons together,” he told me and a small group of Israeli journalists early last year. “In the mind of the Iranian citizen, a link has been created between his economic difficulties and the nuclear project. Today in Iran, there is a profound internal debate about this matter, which has divided the Iranian leadership.” He beamed when he added, “It pleases me that the timeline of the project has been pushed forward several times since 2003 because of these mysterious disruptions.”

Barak and Netanyahu are less convinced of the Mossad’s long-term success. From the beginning of their terms (Barak as defense minister in June 2007, Netanyahu as prime minister in March 2009), they have held the opinion that Israel must have a military option ready in case covert efforts fail. Barak ordered extensive military preparations for an attack on Iran that continue to this day and have become more frequent in recent months. He was not alone in fearing that the Mossad’s covert operations, combined with sanctions, would not be sufficient. The I.D.F. and military intelligence have also experienced waning enthusiasm. Three very senior military intelligence officers, one who is still serving and two who retired recently, told me that with all due respect for Dagan’s success in slowing down the Iranian nuclear project, Iran was still making progress. One recalled Israel’s operations against Iraq’s nuclear program in the late 1970s, when the Mossad eliminated some of the scientists working on the project and intimidated others. On the night of April 6, 1979, a team of Mossad operatives entered the French port town La Seyne-sur-Mer and blew up a shipment necessary for the cooling system of the Iraqi reactor’s core that was being manufactured in France. The French police found no trace of the perpetrators. An unknown organization for the defense of the environment claimed responsibility.

The attack was successful, but a year later the damage was repaired and further sabotage efforts were thwarted. The project advanced until late in 1980, when it was discovered that a shipment of fuel rods containing enriched uranium had been sent from France to Baghdad, and they were about to be fed into the reactor’s core. Israel determined that it had no other option but to launch Operation Opera, a surprise airstrike in June 1981 on the Tammuz-Osirak reactor just outside Baghdad.

Similarly, Dagan’s critics say, the Iranians have managed to overcome most setbacks and to replace the slain scientists. According to latest intelligence, Iran now has some 10,000 functioning centrifuges, and they have streamlined the enrichment process. Iran today has five tons of low-grade fissile material, enough, when converted to high-grade material, to make about five to six bombs; it also has about 175 pounds of medium-grade material, of which it would need about 500 pounds to make a bomb. It is believed that Iran’s nuclear scientists estimate that it will take them nine months, from the moment they are given the order, to assemble their first explosive device and another six months to be able to reduce it to the dimensions of a payload for their Shahab-3 missiles, which are capable of reaching Israel. They are holding the fissile material at sites across the country, most notably at the Fordo facility, near the holy city Qom, in a bunker that Israeli intelligence estimates is 220 feet deep, beyond the reach of even the most advanced bunker-busting bombs possessed by the United States.

Barak serves as the senior Israeli representative in the complex dialogue with the United States on this topic. He disagrees with the parallels that some Israeli politicians, mainly his boss, Netanyahu, draw between Ahmadinejad and Adolf Hitler, and espouses far more moderate views. “I accept that Iran has other reasons for developing nuclear bombs, apart from its desire to destroy Israel, but we cannot ignore the risk,” he told me earlier this month. “An Iranian bomb would ensure the survival of the current regime, which otherwise would not make it to its 40th anniversary in light of the admiration that the young generation in Iran has displayed for the West. With a bomb, it would be very hard to budge the administration.” Barak went on: “The moment Iran goes nuclear, other countries in the region will feel compelled to do the same. The Saudi Arabians have told the Americans as much, and one can think of both Turkey and Egypt in this context, not to mention the danger that weapons-grade materials will leak out to terror groups.