Spurred by a recent United Nations report on Iran's nuclear weapons research, the leading GOP candidates are presenting themselves as hawkish alternatives to Obama and his administration's two-track policy of pressuring and engaging the Islamic republic. They propose more drastic approaches to prevent Iran from developing an atomic bomb - from funding armed rebel movements to launching military attacks.
"If we re-elect Barack Obama, Iran will have a nuclear weapon," Mitt Romney said during Saturday's foreign policy debate in South Carolina. "If you elect me as the next president, they will not have a nuclear weapon."
The former Massachusetts governor and Republican front-runner said the U.S. should be "working with the insurgents in the country to encourage regime change." But, if "there's nothing else we can do besides take military action, then of course you take military action."
The killing of Osama bin Laden, NATO's successful Libya campaign and as-promised U.S. troop drawdowns in Iraq and Afghanistan have helped transform foreign policy into one of Obama's strengths as he prepares for a difficult re-election campaign focused on the economy. Obama has failed to advance Israeli-Palestinian peace talks, but that elusive goal has confounded every American president since Jimmy Carter.
Iran's nuclear program offers an unusual point of attack for the Republican candidates. The paucity of reliable public information makes it hard to assess whether the Obama administration has hampered Iran's nuclear ambitions or allowed their advance, offering plenty of space for GOP candidates to present alternative tactics.
"There are a number of ways to be smart about Iran and relatively few ways to be dumb, and the administration skipped all the ways to be smart," former House Speaker Newt Gingrich said at Saturday's debate. He called for "maximum covert operations to block and disrupt the Iranian program" and backed Romney's call for possible military action. If "the dictatorship persists, you have to take whatever steps are necessary to break its capacity to have a nuclear weapon."
Seeking to one-up Gingrich, longshot candidate Rick Santorum said there "isn't going to be enough time" for tougher sanctions on Iran and more support for pro-democracy groups. He acknowledged the Obama administration's possible involvement in some of the covert attacks on Iran's nuclear program.
But he suggested an even tougher approach alongside Israel to strike Iran's nuclear facilities pre-emptively - similar to the operations the Jewish state conducted against Iraq in 1981 and Syria four years ago. The Reagan administration fumed over the first; the Bush administration acquiesced by silence to the second.
Iran insists its nuclear program is designed solely for peaceful processes, but an International Atomic Energy Agency report last week strongly suggested work toward atomic weaponry. The program has been hindered in recent years by the assassination of Iranian nuclear scientists, a virulent computer virus attacking its facilities and other possible interference - which may or may not have been the result of covert American or Israeli activity.
For all the early talk of engagement, Obama has stuck largely to the Bush administration's latter-year policies of negotiations with Iran alongside international pressure - without the inflammatory rhetoric such as accusations of Tehran's membership in an "axis of evil."
Republicans see the policy nevertheless as a failure and seem to be harkening back to the hard-line American posture taken after U.S. troops toppled Iraq's Saddam Hussein in 2003 and many conservative foreign policy thinkers made Iran's regime the next bogeyman that needed to be taken out.
Then, as now, the argument held that a nuclear-armed Iran would be a mortal threat to U.S. forces in the region and to U.S. ally Israel, whose U.S. backing is wide and deep. Then, as now, the more hawkish voices said time is running out for talking and the U.S. must make clear to Iran that it will use its overwhelming military advantage.
The most likely strategy would be a missile strike on one of Iran's known nuclear facilities, or sabotage from within the country.
Either is clearly within U.S. power, but Obama's calculation has thus far been the same as Bush's: A strike isn't yet worth the risks it carries. Iran could retaliate against U.S. interests or allies, and the Pentagon assesses that if Iran is bent on acquiring a nuclear weapon, a strike would delay but not prevent it.
GOP candidate Herman Cain said he wouldn't pursue a military conflict.
"The only way we can stop them is through economic means," he said.
Libertarian Ron Paul also held back, saying war powers were vested in Congress.
Rick Perry called for sanctions against Iran's central bank to "shut down that country's economy," something the Obama administration has examined in recent months but backed off doing. The fear is that isolating the bank beyond existing U.S. sanctions could drive up oil prices and imperil the fragile world economy.
Over the weekend, Obama argued that U.S. and international sanctions against Tehran have had "enormous bite" and said he'd consult with other nations on further efforts to stop Iran from acquiring an atomic weapon. Without specifically mentioning military action, he insisted, as Bush always did, that U.S. officials "are not taking any options off the table."
Still, the focus is on sanctions. Despite four rounds of economic sanctions against Iran - three during Bush's presidency and the last under Obama - the United Nations is being held back from tougher measures by veto-wielding Security Council members China and Russia. They've offered no sign of a change in posture since Obama's meetings Saturday with Russian President Dmitry Medvedev and Chinese President Hu Jintao.
Romney has argued that Obama made a strategic blunder early in his presidency by failing to leverage Russian support for "crippling sanctions" against Iran before changing the Bush administration's plans for a missile defense system in Europe.
"This is, of course, President Obama's greatest failing from a foreign policy standpoint," he said. "He gave Russia what they wanted, their No. 1 foreign policy objective, and got nothing in return."
Romney's argument is undercut by Bush's similar struggles in rallying global unity against Iran and the assessment by many international security analysts that the sanctions applied under Bush and Obama have seriously undermined Iran's economy.
Responding a day later, Obama said: "Is this an easy issue? No. Anyone who claims it is is either politicking or doesn't know what they're talking about."