The conclusion of a nuclear agreement with Iran, should it happen, will mark only the start of negotiations at home for the White House as it has begun the offensive to sell the deal to a cynical Congress.
Negotiations between Iran and the US-led group of six international powers are approaching a critical moment in Vienna ahead of a self-imposed deadline of today for a final agreement to be reached.
US secretary of state John Kerry voiced concern on Sunday, saying the negotiations "could go either way". The Americans must maintain the strict monitoring of Tehran's nuclear programme set out in the framework deal to ensure Iran uses the development of nuclear power only for energy purposes and not to build a bomb.
The Iranians are pushing for an expedited lifting of economic sanctions.
Opposition
The precariousness of the talks and today’s deadline have fanned opposition at home with Republicans voicing stronger warnings. And not even all Democrats are happy about the talks.
If a deal is concluded today, Congress has 30 days to review it. If an agreement is not reached by Thursday, Congress would have 60 days to consider it.
Republican senator Bob Corker, chairman of the Senate foreign relations committee, raised concerns with Mr Kerry on Saturday about the rush to conclude an agreement, fearing the administration might be too keen to agree a legacy-defining deal.
"Right now, we have the issues of : are we going to have anytime-anywhere inspections, will we know what their past military dimensions were?" Corker told CBS programme Face The Nation.
“I urged him [Kerry] to please take their time, try to make sure these remaining red lines that haven’t been crossed do not get crossed and, qualitatively, they don’t make it worse.”
Even if Republicans and some Democrats object to a deal, Congress will struggle to secure enough votes to override a presidential veto.
“It is very easy to attack a deal that doesn’t yet exist; people who oppose the deal or diplomacy per se are out there controlling the narrative,” said James Acton, co-director of the nuclear policy programme at the Carnegie Endowment for International Peace.
“Once there is a deal that can be defended it is easier for the administration to make the case, and I think the public does not want another war in the Middle East and is in favour of doing any deal.”
The talks have been tricky. The Iranians are said to have agreed to cooperate with an investigation into whether they have secretly tried to develop weapons in the past, but are refusing to allow inspectors to examine all nuclear facilities, including military sites.
