Clinton's comments raised eyebrows because they seemed to go beyond the Obama administration's current thinking on Iran, which has been strictly focused on preventing the country from acquiring nuclear weapons.
Since making the remark on a television chat show in Thailand, Clinton has backpedaled, saying she was only restating existing policy and not referring to any sort of formal guarantees of protection under an American "nuclear umbrella."
And when Israeli officials raised alarms that she seemed to suggest the U.S. was resigned to a nuclear-armed Iran, Clinton and senior State Department officials hastily insisted such a prospect was still unacceptable and that no policy had changed.
But her comments sounded uncannily like the harder-edged "nuclear umbrella" approach toward Iran that Clinton and several other top advisers to President Barack Obama had pushed before they joined his administration.
Bringing both Arab allies and Israel under a protective U.S. "nuclear umbrella" is an idea that has been batted around Washington since fears of Iran's ambitions first percolated in the late 1990s.
Clinton herself raised the notion of such a policy during her unsuccessful presidential campaign last year.
"We should be looking to create an umbrella of deterrence that goes much further than just Israel," she said in an April 2008 debate with Obama. "Of course, I would make it clear to the Iranians that an attack on Israel would incur massive retaliation from the United States. But I would do the same with other countries in the region."
During that debate, Obama affirmed support for Israel's security but did not suggest protecting Arab states.
Some policy experts say Clinton's umbrella reference was simple carelessness. Others wonder if it is indicative of an administration that has yet to show discipline in foreign policy thought and action.
"This is something that a secretary of state, in an academic or off-the-record setting, might muse about," said Aaron David Miller, a former Mideast peace negotiator now with the Woodrow Wilson Center International Center for Scholars.
"But saying it on the road and on-the-record is something else," he said. "It reflects to a certain degree a problem. It reflects a certain confusion in the administration's approach and the absence still of a coherent and cohesive strategy."
During her trip last week, Clinton mentioned a "defense umbrella" during an interview on Thai television Wednesday.
"We want Iran to calculate," she said, "what I think is a fair assessment: that if the United States extends a defense umbrella over the region, if we do even more to develop the military capacity of those (allies) in the Gulf, it is unlikely that Iran will be any stronger or safer because they won't be able to intimidate and dominate as they apparently believe they can once they have a nuclear weapon," she said.
A day later, she insisted to another interviewer that the "defense umbrella" was "nothing specific."
"It is a sort of general term that is used to describe our commitment to making sure that Iran doesn't get a nuclear weapon," she said.