Though they are facing considerable pushback from Congressional Republicans, who largely opposed the deal in the first place, administration officials have informed the Senate that Iran is quickly fulfilling its obligations under the P5+1 deal, and the US may be obliged to lift sanctions earlier than they’d expected.
The US had initially planned on the deal coming through at some point in spring, but following IAEA reports that Iran is quickly implementing all of its requirements, and that they will be in a position to confirm Iran’s full implementation, likely in January.
At that point the US will be obliged to follow through with its own requirements under the deal, lifting sanctions on Iran. Despite previous administration warnings that Iran is “going too fast,” once the IAEA affirms Iran has met its obligations there would be no reasonable basis for the US to keep dragging its feet.
The Rouhani government has been eager to get the deal implemented before the February elections, so that they could campaign on the success of their international diplomacy. Though it was previously seen as unlikely they’d be able to get everything done so fast, it now seems all but certain they will be well ahead of the vote on it.