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As president, Mr. Bush also delivered video Nowruz messages to the people of Iran. In 2002, he explicitly supported the student movement that received international attention after 1999 when protests against the reform government of President Mohammad Khatami shut down Tehran University.

Mr. Sadjadpour said the difference between the current president and Mr. Bush is that Mr. Obama is viewed as having tried to win over Tehran through diplomacy before voicing support for the country’s opposition.

“The big difference between Bush and Obama is that there is a widespread perception, both in Iran and internationally, that Obama really made an effort to engage Iran, but the Islamic republic didn’t reciprocate,” he said. “The focus is no longer Washington’s aversion to diplomacy, it’s Iranian intransigence.”

Andrew Apostolou, a senior program manager at Freedom House who works closely with Iranian dissidents, said the shift in Mr. Obama’s tone is significant.

“It is an important change,” he said. “President Obama has moved from seeking to repair relations with the Iranian regime to advocating for political prisoners in Iran.”

Mr. Apostolou also noted that Mr. Obama “explicitly linked the protest movement in Iran in 2009 to the protests sweeping Arab countries in 2011 — which means that the president of the United States is now repeating what Arab democracy activists have said. The message to the Iranian regime is that it is wrong to believe that it can escape the changes elsewhere in the Middle East.”

Mr. Obama, at least publicly, appeared during most of 2009 to be interested in striking a deal with President Mahmoud Ahmadinejad. The White House position on talks with Iran contrasted with the public statements of the democratic opposition that regarded Mr. Ahmadinejad as illegitimate and the beneficiary of a stolen election.

Still, there are signs that behind the scenes that Mr. Obama allowed a nuclear sabotage program launched under Mr. Bush to continue its work. That top-secret program, first reported by the New York Times, was likely the springboard for the Stuxnet computer virus that reports say damaged the computer industrial control systems linked to Iranian nuclear centrifuges by speeding up their rotors, causing them to break down.

A revised intelligence estimate of Iran’s nuclear program — which might be adjusted depending on the success or failure of the Stuxnet virus — is being circulated in secret within the U.S. government.