Editor's note: Joe Cirincione is president of Ploughshares Fund, a global security foundation that seeks to make progress toward a world free of nuclear weapons and author of "Bomb Scare: The History and Future of Nuclear Weapons."
(CNN) -- The strategic calculus for dealing with Iran's nuclear program has shifted dramatically in the past month.
First, came news that the Stuxnet computer worm had apparently wrecked more than one fifth of the centrifuges Iran has used over the past five years to enrich uranium.
Then came new estimates from leading Israeli authorities that Iran is three to five years away from having a nuclear weapon, a sharp shift from earlier assessments. On Sunday, The New York Times reported the U.S. and Israel may be behind the computer virus, confirming what many had suspected.
The nuclear clock is still ticking in Iran. Its scientists and engineers are smart and dedicated, and the regime seems determined to acquire nuclear technology that can be used to make fuel for reactors or the cores of nuclear weapons. But the clock has slowed. Time is now on the side of efforts to negotiate an end to Iran's program.
Credit must be given to the Obama administration. The president's critics have blasted his Iran strategy, portraying him as weak and naive. Some have been campaigning for military strikes as the only solution to a threat they have claimed was urgent and otherwise unstoppable.
Weekly Standard Editor Bill Kristol, for example, has long urged U.S. and Israeli attacks on Iran and blasted President Obama for having "done nothing effective [and] pressuring Israel not to act to stop Iran from getting nuclear arms."
The president, however, now appears to have been playing a deeper game than critics understood.
The strategy could be called "Engage, Sanction and Sabotage." It began two years ago with Obama's offer to talk directly to the Iranian regime as he extended the hand of friendship in his inaugural address.
When Iran rebuffed his calls, Obama used their refusal to build the case for tougher international sanctions, an effort greatly aided by his exposure in September 2009 of a covert enrichment facility near the city of Qom. The U.N. Security Council last year passed the toughest sanctions ever enacted on a member state. The European Union, Japan, South Korea and other states piled on their own sanctions, as did the United States.
Concurrently, the administration, as the Times reports, was developing the most sophisticated cyberweapon ever deployed in "a joint American and Israeli effort to undermine Iran's efforts to make a bomb of its own." It worked.
The centrifuge program was already problematic, working with a decades-old Pakistani design that is notoriously temperamental, resulting in hundreds of machines breaking down. The Institute for Science and International Security concludes that the virus caused new "major problems," forcing the Iranians to remove an additional 984 machines -- known as IR-1 centrifuges -- from their main facility at the city of Natanz.
The sanctions make it much harder for Iran to recover from the cybersabotage. They hamper Iran's ability to import the high-tech materials, such as carbon fiber and maraging steel, needed to replace these machines or build the more advanced centrifuges Iran desires.
A senior European official told the Wall Street Journal, "We believe they are experiencing critical shortages" of the materials for the centrifuges program.
U.S. expert David Albright adds, "They seem to be approaching their limit on the number of IR-1 centrifuges they can build."
Israel's retiring intelligence chief, Meir Dagan, said the international sanctions and covert actions have slowed the Iranian program.
He estimated Iran could not have a nuclear bomb before 2015, while Deputy Prime Minister Moshe Yaalon puts the danger date at 2013. This is a sharp break from previous Israeli estimates that have warned Iran could get a nuclear bomb within months.
The Israeli estimates are a vote of confidence in Obama's Iran strategy. It is by far the most successful Iran policy in decades. The question now is how to use the time?
The nuclear program has been slowed but not stopped. The sanctions are hurting Iran's economy, but the regime has a high pain threshold.
Sanctions and sabotage alone cannot coerce Iran into either compliance or collapse. The 2012 presidential campaign will likely spur renewed calls for military strikes on Iran, as may hearings in the Republican-controlled House of Representatives.
Now is the time to emphasize the engagement component of the strategy.
A new report from the Henry L. Stimson Center and the U.S. Institute of Peace concludes that the administration "must rebalance" its approach.
"U.S. and European leaders should communicate a comprehensive picture of what Tehran has to gain from a mutually acceptable agreement," say authors Barry Blechman and Daniel Brumberg.
In other words, give the Iranian regime a face-saving way out. Pressures are building on Iran and within Iran, but unless the regime believes there is a negotiated solution that can guarantee its security and allow a resumption of normal diplomatic and economic relations -- including with the United States -- the leadership will persist with its current course.
Diplomatic solutions have their risks. But they are far preferable to the risks of war with Iran. Or the risks of an Iranian response to the cyberwar we are apparently now waging. Now is the time to press the U.S. advantage and capitalize on the gains the administration has won.
The opinions expressed in this commentary are solely those of Joe Cirincione.