Iran and the six major powers may be within reach of an agreement to limit Iran’s nuclear program. After months of little apparent progress, the quickening pace of talks suggests that negotiators in Geneva might be able to complete a framework by the end of March, with a final accord reached at the end of June. This isn’t certain, but it offers hope that the protracted nuclear threat from Iran can be resolved peacefully.

If it comes together, any agreement would have to establish verifiable limits on the nuclear program and ensure that Iran cannot quickly produce enough weapons-usable material for a bomb. A pact would not end Iran’s nuclear program outright, which it says it needs for power generation and medical purposes, or erase the nuclear know-how Iran and its scientists have acquired over the nearly 60 years since an agreement between President Eisenhower and Shah Mohammed Reza Pahlavi for the United States to provide Iran with nuclear technology.

Critics of any deal — including those in Congress, such as Senator Mark Kirk, a Republican of Illinois, and Senator Robert Menendez, a Democrat of New Jersey; and Prime Minister Benjamin Netanyahu of Israel — demand complete dismantlement of Iran’s program given the country’s history of lying about its efforts to produce nuclear fuel and pursue other weapons-related activities.

But their desired outcome simply cannot be achieved. President George W. Bush wasn’t able to secure that goal in 2003 when Iran had only a few dozen centrifuges, the machines that enrich uranium for nuclear fuel. Now, 12 years later, Iran has an estimated 19,000 centrifuges, not to mention scores of other facilities, including some that have been hardened to withstand a military attack.