American intelligence officials say that they learned a traumatic lesson from the Iraqi weapons debacle, and that assessments of Iran’s nuclear program are hedged and not influenced by political or policy considerations…

In assessing the construction near Qum, the Central Intelligence Agency “formed its conclusions carefully and patiently over time, weighing and testing each piece of information that came in,” said Paul Gimigliano, an agency spokesman. “This was a major intelligence success.”

Not all are persuaded. Glenn Greenwald, an author and a left-leaning blogger for the online magazine Salon, called the parallels with the charges that Iraq had so-called weapons of mass destruction in 2002 “substantial and disturbing.”…

“Some people are saying time’s running out and we have to act by the end of the year,” said Mr. Thielmann, now a senior fellow at the Arms Control Association. “I’ve been arguing that we have years, not months. The facts argue for a calmer approach.”