Robert Wright points out why a first-term President Mitt Romney would be more susceptible to hardline pressure on Iran than a second-term President Barack Obama:
Second-term presidents think legacy, and nothing says legacy like peacefully and enduringly solving a problem that’s been depicted as apocalyptic. So expect Obama to pursue serious negotiations with Iran (which he hasn’t really done yet) if he wins the election. And he’ll be able to pursue them liberated from concerns about re-election, which means he can largely ignore blowback from Bibi Netanyahu, AIPAC, and other elements of the Israel lobby. That sort of freedom is important if he wants to bargain seriously with Iran.
Any first-term president who hopes for re-election (that is, any first-term president) is mindful of lobbies, whether the sugar lobby, the Cuba lobby, or the Israel lobby. So any new president would likely have a harder time peacefully solving the Iran problem than a second-term President Obama. But for Romney this disadvantage is compounded by two factors.