The framework deal on Iran's nuclear program has come under heavy scrutiny as the Obama administration seeks to sell the agreement to skeptical lawmakers.
Many of the terms mark a shift from President Obama's stated goals at the start of negotiations 18 months ago.
But Republican critics say the administration made concessions that go too far and secured little in return.
Here are five areas where the administration shifted course during negotiations:
1. Banning uranium enrichment
Before talks began, the Obama administration and the United Nations Security Council called for Iran to stop all uranium enrichment.
The framework agreement, though, allows Iran to continue enriching uranium and producing plutonium for domestic civilian use.
"Zero enrichment" had been a key demand since 2009, said Michael Singh, a senior fellow and managing director at The Washington Institute. “We basically went from zero to a number that kept going up."
The deal's critics worry any enrichment could quickly be diverted to military use.
Omri Ceren, senior adviser for strategy at the Israel Project, said the administration started "sliding" on zero enrichment after talks began.
But U.S. officials have suggested that halting all enrichment was never a realistic goal, and instead a key bargaining chip to secure other concessions from Iran.
“As soon as we got into the real negotiations with them, we understood that any final deal was going to involve some domestic enrichment capability," a senior U.S. official told the Wall Street Journal last week. “But I can honestly tell you, we always anticipated that.”
Reza Marashi, research director at the National Iranian American Council and a former State Department official, said the U.S. had to budge on this demand for the talks to advance.
“It was the icebreaker. It was what allowed these negotiations to take root,” he said.
He said it led to key concessions from Iran, including unprecedented inspections of nuclear facilities.
“It’s the single most important point in my opinion, in terms of getting negotiations off the ground," he said. "Once that position softened, it allowed the Iranian position to soften.”
2. Capping centrifuges at 1,500
The Obama administration initially called for limiting the number of Iranian centrifuges used to enrich uranium to between 500 and 1,500, experts say.
But U.S. negotiators walked back those limits, allowing Iran 6,104 centrifuges. Only 5,060 of those centrifuges, at the nuclear facility at Natanz, will be allowed to enrich low-grade uranium.
“The number [went] from hundreds, to thousands, to eventually, 6,104, which is where they ended,” said Singh.
Critics balked at the framework figure, noting Iran would have four times as many centrifuges as Obama hoped to allow.
But proponents of the deal say it is still a huge two-thirds reduction from Iran's current 19,000-some centrifuges, and that any enriched uranium would be unusable for a bomb.
They also argue the more important criteria is not the number of centrifuges but the time it takes Iran to have enough material for a bomb — the ”break-out” period — which the framework leaves at one year.
Marashi said expanding the number also led Iran to agree to only use older so-called first-generation centrifuges.
“This is critical, because now we know the exact infrastructure, we know the exact output, we know the exact number of centrifuges so there’s no mystery,” he said.
3. Shuttering secret nuclear facilities
The U.S. initially called for Iran to completely close down its secret underground nuclear enrichment facility at Fordow and the heavy water reactor at Arak.
President Obama said in December 2013 that Iran had no need for either.
“They don’t need to have an underground, fortified facility like Fordow in order to have a peaceful nuclear program,” he said. “They certainly don’t need a heavy-water reactor at Arak in order to have a peaceful nuclear program."
However, under the framework announced last week, both Fordow and Arak remain in operation. Fordow will have 1,000 centrifuges but be converted into a research facility, wile Arak will continue producing plutonium, albeit at a low-grade unusable for a bomb.
“We had always, always, always said that Fordow must be closed,” said Ceren. “That was always the plan. We collapsed on that.”
Officials, though, say the facilities will no longer contribute to a weapons program.
Fordow will not enrich uranium or keep any fissile material there for at least 15 years, and almost two-thirds of its centrifuges and infrastructure would be removed and placed under International Atomic Energy Agency (IAEA) monitoring.
Also, Iran has agreed to implement the "Additional Protocol of the IAEA" which would provide inspectors expanded and regular access to Iran's facilities and nuclear supply chain.
Marashi said it was painful for the U.S. to allow Fordow and Arak to remain open, but stressed that the facilities would be reconfigured for peaceful purposes.
Skeptics, though, say Iran could continue covertly working on a bomb, noting that Fordow is underground and heavily fortified.
“There was certainly a sense that we were seeking to sort of shut down or dismantle Iran’s nuclear program in a significant ways,” said Singh. “Under this deal, there’s certainly no dismantling of any kind."
4. Ending Iran's ballistic missile program
U.S. negotiators also dropped demands that Iran restrict development of ballistic missiles that could be used to deliver warheads, experts say.
The current framework only says a new U.N. resolution would incorporate “important restrictions on conventional arms and ballistic missiles.”
“They have completely given up ballistic missiles," Ceren said.
The Obama administration says the issue of missiles and other conventional weapons should be treated separately from the nuclear deal.
“As we’ve said, we have concerns about Iran’s conventional weapons, including ballistic missiles, separate from the nuclear program, obviously,” State Department spokeswoman Marie Harf said Wednesday.
“Those concerns don’t go away with the nuclear agreement," she added.
Marashi said the ballistic missile issue was something opponents of diplomacy tried to force into the negotiations.
Singh, though, called the issue critical.
“It’s treated like a side issue, but it really shouldn't be treated as a side issue because obviously, long-range ballistic missiles are essential to a nuclear weapons program,” he said.
5. Finalizing a 20-year deal
Initially the U.S. pushed for a deal that would last over 20 years. However, the framework would see the deal’s key terms sunset in 10 to 15 years.
Specifically, Iran would have to restrict the number of centrifuges enriching uranium for 10 years. In addition, the level of uranium enrichment would be capped at a lower-quality grade and the amount Iran stockpiles limited for 15 years.
In addition, the restrictions on Fordow and Arak also last for 15 years.
Ceren said even though Iran isn't legally allowed to build a bomb, all "functional" restrictions on Iran’s nuclear capacity would be lifted after 15 years.
“For many months, we’ve said we’ve wanted a 25-year sunset clause, then a 20-year sunset clause, now we’re down to a 10-year sunset clause,” Ceren said.
Administration officials pushed back against the idea that the deal sunsets at all.
Energy Secretary Ernest MonizErnest MonizWhat we learned from Rick Perry's confirmation hearing Overnight Energy: Rough hearing for Tillerson Overnight Energy: Former Exxon chief Tillerson takes the hot seat MORE characterized it as a "forever agreement," with terms forcing Iran to be transparent about its program and ensuring the international community can always keep a close eye.
Marashi predicted the final deal will include "permanent transparency measures that go beyond" the IAEA's requirements.
"So yes, some of the limitations that Iran will agree to will come off after 10 to 15 years. But even when those things come off, Iran will still have the most heavily inspected nuclear program in the history of the world,” he said.
Some supporters also say the next decade could herald a thaw in U.S.-Iran relations. But skeptics are unsold.
"If nothing changes in Iran in 10 years ... then you're looking at after 10 years, a much shorter break-out time,” Singh warned.