"Given the dire situation in the region, with civil war in Syria, Iraq still very unstable, Arab Spring spreading to Bahrain and Yemen, Iran is seeing that instability in the region requires less hardline positions and to be at least at the table and have a voice," Qamar-ul Huda, a senior program officer at the U.S. Institute of Peace, said.
Either way, it looks like sanctions at least did something, so more would probably be even better.
That's the argument lawmakers of both parties are making, but it may not be that simple.
"It was strong sanctions, not the goodness of the hearts of the Iranian leaders, that brought Iran to the table," Sen. Charles Schumer, D-NY, said in a statement arguing for tougher measures, as reported by ABC News.
Senate Majority Leader Harry Reid, D-Nev., likewise said in a Monday radio appearance that the Senate would consider more sanctions when it returns in December, as reported by The Hill, and Sen. Marco Rubio, R-Fla., also said the U.S. should turn up the heat on Iran.
Yet while ramping up sanctions could hurt Iran, it could also hurt the U.S. in its relationship with some allies.
"Particularly important here is China and India," says Schott. Those countries have received a waiver to purchase oil from Iran under the current sanction regime, but in return must prove to the U.S. that they are reducing their purchases from Iran. One side effect of this deal is "taking the pressure off" of China and India. Were the U.S. to ramp up sanctions instead, he says, it could ramp up that pressure on China and India, creating new international tensions.
The very fact that the recent "stick" of sanctions on banking and oil have worked – not to mention the "carrot" of easing a few of those sanctions – is a reason to remain watchful and hopeful during the next round of talks, says Schott.
"Whether the carrot is enough to get them to follow through on these commitments and go to the next level...we'll have to see, and that's where a lot of the skepticism is on the Hill," he says.