ABC News' Tahman Bradley reports:
The single most important test of American power in the Middle East is whether the U.S. is successful in stopping Iran from acquiring nuclear weapons capability, Sen. Joe Lieberman, I-Conn., told the Council on Foreign Relations today in Washington, DC. Senator Lieberman said military force is not the ideal way to handle Iran's nuclear ambitions, but it should remain on the table.
"If nuclear Iran is as dangerous as we say, we must take action to stop them from acquiring a nuclear weapon," he said.
Calling it "unacceptable" for Iran to acquire a nuclear weapon, Lieberman said the world will judge the United States on its success or failure stopping Iran's ambitions.
"Some have suggested that we should simply learn to live with a nuclear Iran," Lieberman said. "In my judgment, that would be a grave mistake. And as one Arab leader I recently spoke with pointed out, how could anyone count on the United States to go to war to defend them against a nuclear Iran, if we were unwilling to go to war to prevent a nuclear-armed Iran in the first place?"
Lieberman said the time has come for the U.S. to step up pressure on Iran if it becomes clear that sanctions against the country will not work
"As long as centrifuges are spinning and uranium is enriching, the pressure on Iran must grow," he said.
Lieberman hopes President Obama will make an assessment of the current Iran strategy by the end of the year. He also wants the U.S. to lead the international effort to reign in Iran.
"If military action must come, the United States is in the strongest position to confront Iran and manage the regional consequences. This is not a responsibility we should outsource."
Asked by ABC News' Senior Congressional Correspondent Jon Karl, who moderated the event, if President Obama has done a sufficient job laying the groundwork for a potential conflict with Iran, Lieberman refused to criticize the Obama administration even though his remarks seemed to suggest he hopes the U.S. takes an even harder stand on Iran.
"The actions of this administration -- particularly on the sanctions front -- have been very aggressive, and I give them a lot of credit for that," said Lieberman.