Extract from a NYT article
WASHINGTON – New York Times – NOV. 16, 2014  — When President Obama wrote last month to Ali Khamenei, urging him to overcome a decade of mistrust and negotiate a deal limiting Tehran’s nuclear ambitions, it was perhaps the president’s last effort to reach a reconciliation with Iran that could remake the Middle East.
Today, Mr. Obama needs a foreign policy accomplishment more than ever, and he sees time running out on his hope of changing the calculus in a Middle East where Americans are, against his instincts, back on the ground. But the forces arrayed against a deal are formidable — not just Mr. Khamenei and the country’s hard-liners, but newly empowered Republicans, some of his fellow Democrats, and many of the United States’ closest allies.
Mr. Obama’s top national security advisers put the chance of reaching an agreement this month at 40 to 50 percent.
“In the end this is a political decision for the Iranians,” Mr. Obama told a small group of recent visitors to the White House, a statement that could be true for him as well.

Yet even if a deal is struck it will be the beginning of an argument, rather than the end of one.
“In every nation involved, this negotiation is a proxy for something bigger،” argues Robert Litwak, a Wilson Center scholar and author of “Iran’s Nuclear Chess: Calculating America’s Moves.”
“Here it is a test of Obama’s strength and strategy،” he said. “In Tehran it is a proxy for a fundamental choice: whether Iran is going to continue to view itself as a revolutionary state, or whether it’s going to be a normal country،” which so many of its young people yearn for it to become.

The Saudis have a parallel worry. No one has been more outspoken on the issue than Saudi Arabia’s former intelligence chief, Prince Turki bin Faisal, who in recent weeks has warned that the Saudis will build uranium enrichment facilities to match whatever Iran is allowed to retain — even if the kingdom has no use for them. That has raised the specter of an arms race, even if a deal is struck.

The notable exception are the French, who have publicly argued for tougher terms in the negotiations and say they see their role as to serve, in the words of one Western diplomat, as “a significant counterweight on the impulse of Obama to make concessions.”
But the biggest counterweight to a negotiating success with Iran may be the new Republican majority in the Senate — including some members, like Senator Lindsey Graham, who have argued that Mr. Obama is overly eager for a deal.
Obama administration officials reject the charge and say that though Mr. Obama is hopeful, he would never sign an accord that did not put Iran a year or more away from being able to produce enough fuel for a single bomb. “Whatever we negotiate we will have to sell in Congress, sooner rather than later,” said one of Mr. Obama’s senior strategists, declining to speak on the record because of diplomatic sensitivities.
“And that works to our advantage in the negotiating room, because it means we can say to Zarif,” the Iranian foreign minister, “Even if we agreed to lifting sanctions early, or letting you keep all your centrifuges in place — and we wouldn’t — Congress would rebel.”
That rebellion has started. When Congress came back into session last week Senator Robert Menendez, the New Jersey Democrat who leads the Senate Foreign Relations Committee, and Senator Mark Kirk of Illinois issued a statement saying that “as co-authors of bipartisan sanctions laws that compelled Iran to the negotiating table, we believe that a good deal will dismantle, not just stall, Iran’s illicit nuclear program and prevent Iran from ever becoming a threshold nuclear state.” They would enact new sanctions “if a potential deal does not achieve these goals.”
It is a view the new Republican majority will back, along with many Democrats. Mr. Obama could always veto new sanctions, but the warnings themselves may make it harder, administration officials fear, to get Iran to reach a final agreement.

“What the Iranians are looking for is a narrative of victory،” one American diplomat said last week, “a way to say the West backed down, and admitted Iran will be able to produce its own nuclear fuel one day, in unlimited quantity.” What Congress needs, the diplomat said, “is a narrative that Iran was forced to dismantle what it has.”
Satisfying both, he added, “is what makes the politics of this so much harder than the physics of slowing the bomb program.”
David E. Sanger reported from Washington, Steven Erlanger from London, and Jodi Rudoren from Jerusalem.