Iran hasn't decided whether to accept a proposal to export most of its enriched uranium to Russia, but the Obama administration is said to be quietly optimistic that it has finally broken the atomic deadlock with Tehran. Is the optimism justified?

Maybe, but only somewhat:
While the agreement on the table "would be a move in the right diplomatic direction," it would not force Iran to freeze its existing enrichment program, says Con Coughlin in Britain's Telegraph. "So far the Iranians have carefully avoided discussing (that), and until they do so a resolution of the nuclear crisis will continue to remain elusive."
"Is Tehran beginning to thaw?"

Yes, thanks to Obama: The deal still "could all fall apart," say the editorial writers at Britain's The Guardian. But if it succeeds, "it will show that Barack Obama has obtained more from Iran in a few hours of talks than George Bush did during eight years of rhetorical confrontation."
"Iran: Nuclear fission"

No, and it’s Obama’s fault: Iran will never negotiate, former senator Rick Santorum says in the Philadelphia Inquirer, so Obama will be left to "accept a nuclear Iran (or) deal with the consequences of an Israeli strike on Iran's nuclear facilities."
"Obama’s failing Iran policy"

Never, military action is the only solution: "The president, so intent on rejecting the eight years of Bush, is ignoring important history," Bush’s former UN ambassador John Bolton tells the National Review. "Negotiations or sanctions won’t work ... The real choice, though an unattractive option of course, is the use of force."
"Bolton: Obama’s ‘virtual reality’"