In the dead of night Wednesday night in Lausanne, Switzerland, Energy Secretary Ernie Moniz and his Iranian counterpart haggled over one of the last issues holding up a nuclear agreement with world powers: Iran’s future research into next-generation new centrifuge designs that can accelerate its path to a nuclear weapon. 
 
 The meeting finally wrapped up at 6 a.m., said a senior administration official, “and that is not because we were up early.” 
 
 But how that key issue was resolved remains fuzzy. An Obama administration fact sheet on the deal says only that Iran will be able to conduct “limited research and development” into the centrifuges — which are far more efficient than the relatively crude devices Iran now operates — “according to a schedule and parameters which have been agreed to” by Iran, the United States, and five other world powers. 
 
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 Although Iran will be barred for a decade from enriching uranium with the advanced devices, that schedule and those parameters remain otherwise unknown. 
 
 Critics of the agreement were quick to zero in on the question. “This is a bad framework that will lead to a bad and dangerous deal,” said an Israeli government source in Jerusalem, who cited as a key complaint the fact that Iran “will continue its centrifuge research and development.” 
 
 The research-and-development question is just one of a handful of key issues left unresolved, at least in public, and which could endanger the agreement’s survival. 
 
 There was much for Obama officials — and their negotiating partners in France, Germany, Britain, China and Russia — to be happy about in the framework deal, whose details must be nailed down by June 30. It requires Iran to uninstall more of its centrifuges than earlier reports had suggested would be required. It subjects Iran to extensive snooping by international inspectors, with some surveillance extending for 25 years. It mandates the redesign of a nuclear reactor so that its spent fuel can’t be used to make a bomb. 
 
 But the White House and State Department will find themselves defending some questions the agreement essentially fudged. 
 
 In addition to the centrifuge research, another key issue is the fate of Iran’s stockpile of low-enriched uranium. That is material which has been enriched much of the way toward the purity needed for a nuclear weapon, therefore making it dangerous for Iran to possess. 
 
 The administration’s fact sheet says Iran must “reduce” that supply of nuclear material, from more than 10 tons currently on hand to just a few hundred pounds — less than enough to create a bomb. 
 
 But it doesn’t specify how that will happen. U.S. officials had long expected that Iran would agree to export most of its low-enriched uranium out of the country, ensuring that it can’t be diverted to military use. Late in the talks this week, Iran toughened its position, insisting that it would merely dilute that uranium on its own soil to a form unsuitable for weapons use. 
 
 Thursday’s deal punts that question for later. At a news conference in Lausanne, Secretary of State John Kerry said Iran had committed to selling the material on the international market or diluting it to a harmless state. But critics of the deal noted that diluted uranium can still be converted to a more dangerous form. 
 
 Some nuclear experts downplayed the stockpile issue, however. 
 
 Jofi Joseph, a former national security council aide in the Obama White House who handled nuclear nonproliferation issues, said it would be laborious for Iran to reconvert its uranium. 
 
 “It’s more a question of political optics,” Joseph said. ““Remember, it’s important politically for Iranian leaders to not be seen as ‘surrendering’ anything, which is why they fought so hard against export.” 
 
 That point was echoed by a senior Obama official on Thursday, speaking more generally about the deal: “There is no doubt that [Iranian Foreign Minister] Javad Zarif will have to sell this deal just as we will. And his task is hard and complicated.” 
 
 Likely to be most problematic of all is Iran’s response to questions about its past research into nuclear weapons production, including bomb designs and detonators. The International Atomic Energy Agency says that Iran has stonewalled on all but one of a dozen questions the agency has posed. Iran has denied the IAEA access to its Parchin military base, where the United Nations nuclear watchdog group suspects it tested explosives that could be used to detonate a bomb. 
 
 Iran denies it has ever pursued a military application to its nuclear program. But U.S. intelligence officials say they are confident Iran aggressively researched bomb-making until 2003, when that aspect of its program was halted. 
 
 Thursday’s agreement is vague on this score. The fact sheet says only that Iran “will implement an agreed set of measures to address the IAEA’s concerns,” but those measures aren’t detailed. 
 
 The past research into bomb-making “appears to be one of the few Achilles’ heels here,” said Joseph. On that point, he added: “It doesn’t appear as if Iran agreed to do anything specific.” ||||| Key players in Congress -– Republicans and Democrats -- are skeptical of the Iran deal and want to see the fine print. 
 
 No one is ruling out a big push ahead on new Iran sanctions, or a measure to require President Obama to get congressional approval, two pieces of legislation the White House strongly opposes. 
 
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 But there appears to be a willingness to hear the administration out in promised briefings on the framework when lawmakers return to Washington on April 13. 
 
 An aide to House Speaker John Boehner tells ABC News that the approach in the House is not a “wait-and-see until June 30th” posture, but that Republicans want the briefings, a chance to review the details and discuss possible next steps with members. 
 
 Sen. Bob Corker, chairman of the Senate Foreign Relations Committee, said today “it is important that we wait to see the specific details of today’s announcement” and that everyone “must remain clear-eyed.” He vowed an April 14 committee vote on a bill to require congressional review of a nuclear deal, but there is no plan yet to bring it up for a vote in the full chamber. (Corker has said he’d like to have a veto-proof majority before the bill is voted on by the full Senate.) 
 
 “We’ll know more in the days ahead, after April 14,” an aide to Senate Majority Leader Mitch McConnell told ABC News. 
 
 Rep. Adam Schiff, the top Democrat on the House Intelligence Committee, said he was surprised so many details were revealed in the framework and said that Congress should “be careful not to scuttle the opportunity for a diplomatic resolution. 
 
 “I think there is sufficient detail that has been arrived at these negotiations that Congress needs to be careful not to scuttle the opportunity for a diplomatic resolution,” Schiff said in an interview. “The last thing we want is for the international community to think that we came this close to a negotiated end to Iran’s nuclear program and the United States Congress got in the way.” 
 
 Sen. Tom Cotton, R-Arkansas, the author of the controversial open letter to Iran's leaders signed by 47 Republican senators, called the interim deal a "list of very dangerous U.S. concessions that will put Iran on the path to a nuclear weapon." 
 
 “I plan to work with all of my colleagues on both sides of the aisle who have already expressed disquiet about terms such as these, to stop this deal from going forward, to keep America safe, and to prevent a nuclear arms race in the Middle East,” he added. 
 
 Sen. Marco Rubio, R-Florida, who is likely weeks away from announcing a presidential bid, tweeted his skepticism of the deal, but said he is awaiting more information. 
 
 Awaiting more details on #Iran deal but early reports indicate this is Obama admin spinning diplomatic failure. — Marco Rubio (@marcorubio) April 2, 2015 
 
 The White House fired another warning shot this afternoon reiterating veto threats for any legislation that “undercuts our ability to get the deal done.” 
 
 “We think it’s best for members of Congress to take a look at the framework and then give the space to look at final details between now and June,” said deputy national security adviser Ben Rhodes. 
 
 Congress needs to “wait and see what the deal is, and then we can determine the best way to support Congress playing an oversight role,” he said. ||||| WASHINGTON — Leading lawmakers from both parties in Congress responded cautiously on Thursday to the tentative framework for a nuclear deal between Western powers and Iran, demanding to review any final agreement but pointedly refraining from a vow to kill the accord. 
 
 Congress could still scuttle a deal if lawmakers move forward with tough new sanctions on Iran just as economic and nuclear penalties are supposed to be lifted. And Senator Bob Corker of Tennessee, the chairman of the Senate Foreign Relations Committee, said the panel would continue with plans to formally draft bipartisan legislation on April 14 insisting on congressional examination of any agreement. 
 
 The committee’s leadership was looking for ways to shape a bill that would gain broad approval in both parties. 
 
 “We want the right to go through the details of the deal and to decide whether we believe congressionally mandated sanctions should be alleviated,” Mr. Corker said in an interview. 
 
 That sentiment was bipartisan. 
 
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 “If Congress appears to be bypassed, that’s not good for the national debate and national unity as we move forward with Iran,” said Representative Eliot L. Engel of New York, the ranking Democrat on the Foreign Affairs Committee. 
 
 President Obama made a pointed appeal to Congress to let diplomacy work, even as he promised consultation. 
 
 “If Congress kills this deal — not based on expert analysis, and without offering any reasonable alternative — then it’s the United States that will be blamed for the failure of diplomacy,” he said at the White House. “International unity will collapse, and the path to conflict will widen.” 
 
 But a senior administration official hinted at compromise, at least on the review legislation. He reiterated the president’s promise to veto legislation imposing new sanctions on Iran, but said that a previous veto threat on the congressional review bill applied only to the measure as it was originally drafted. 
 
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 The jousting is likely to continue for months, and pressure could mount on Republican leaders to toughen their stand. Negotiators must turn a framework into a detailed agreement by this summer, and legal sanctions imposed by the United States will not have to be lifted anytime soon, possibly not for years. The agreement is not likely to require action from Congress until the next presidential administration. 
 
 But beyond the leadership suites, a more hard-edge response came quickly. 
 
 “The Obama administration’s efforts to get a deal at any cost will have a greater cost than the world can bear,” said Representative Michael McCaul of Texas, the chairman of the Homeland Security Committee. “If this deal moves forward, the consequences for the U.S. and our allies in the region will be dire.” 
 
 Some Democrats hailed it. “We’ve set the stage for a paradigm shift in the country and in the region,” said Representative Earl Blumenauer, Democrat of Oregon. 
 
 But other Democrats tried to find a middle ground between embracing the accord and undermining it. Senator Benjamin L. Cardin of Maryland, the ranking Democrat on the Foreign Relations Committee, said that he wanted unanimity around Congress’s request for review, and that aspects of the legislation would have to be toned down. 
 
 The bill demands that the administration submit the full text of any agreement to Congress, including classified annexes. It would prohibit the removal of any congressional sanctions for 60 days after a final accord, and would require the president to certify Iranian compliance every 90 days. Without that certification, it mandates a quick return of sanctions. 
 
 The original version was written by Mr. Corker and Senator Robert Menendez, Democrat of New Jersey, a hard-liner on the Iran talks. But Mr. Menendez’s indictment Wednesday on corruption charges, and his decision to step down from the top Democratic spot on the Foreign Relations Committee, elevated the more diplomatic voice of Mr. Cardin. 
 
 “The more unity we can have among Democrats and the White House, the stronger U.S. foreign policy will be,” Mr. Cardin said. 
 
 In general, the most senior Republicans, while cool to the deal, spoke in measured tones. “In the weeks ahead, Republicans and Democrats in Congress will continue to press this administration on the details of these parameters and the tough questions that remain unanswered,” said the House speaker, John A. Boehner of Ohio. “We will stand strong on behalf of the American people and everyone in the Middle East who values freedom, security and peace.” 
 
 The biggest question is not about the congressional review legislation but about whether Republican leaders will try to resurrect House and Senate measures that would impose tough new sanctions on Iran. Both versions have had broad bipartisan support, but their passage could imperil a final deal. 
 
 “There will be a move to apply new sanctions or deprive the president of the ability to waive existing sanctions,” said Representative Brad Sherman, Democrat of California and a senior member of the House Foreign Affairs Committee. While that inclination is present in both chambers and in both parties, he said, “the tendency will be to vote for or against the president based on party.” 
 
 Mr. Obama, announcing the tentative accord in the White House Rose Garden, said the issues at stake were “bigger than politics.” 
 
 “These are matters of war and peace, and they should be evaluated based on the facts and what is ultimately best for the American people and for our national security,” he said. 
 
 But lawmakers in both parties asked pointed questions about the framework presented. Mr. Corker said that he believed sanctions would be lifted too quickly, and that he wanted to better understand what would happen to Iran’s fissile nuclear materials. Mr. Engel was pleased that Iran’s array of centrifuges would be reduced by two-thirds, and that inspections of uranium mining and milling would last 25 years. 
 
 “But tell me why Fordo remains open,” he said, referring to Iran’s underground enrichment site. “Why not just destroy it?”
– A blueprint outlining the path toward a final deal between Western countries and Iran on its nuclear program was drafted yesterday, and Politico notes "there was much for Obama officials" and their partner countries to "be happy about," such as more centrifuge disassembling than previously anticipated. But there are still tenuous points that need to be fleshed out and an American public that needs convincing, and a congressional committee intends to create a bipartisan bill on April 14 that would demand congressional review of any deal, the New York Times notes. An aide for Speaker John Boehner tells ABC News that "a wait-and-see until June 30" (the deadline for a full agreement) approach isn't in the cards, while Sen. Bob Corker tells the Times "we want the right to go through the details of the deal and to decide whether we believe congressionally mandated sanctions should be alleviated." Keeping the agreement's framework shaky is the lack of detailed schedules and logistics on certain key points, including nuclear R&D and a uranium-reduction program, Politico notes. The bill would insist on a full review of all agreement text, ban the removal of sanctions for 60 days after a final deal is reached, and mandate that the president check up on Iran's compliance every 90 days, the Times notes. But while lawmakers on both sides are touting compromise, there are still the hardballers. "I plan … to stop this deal from going forward," Sen. Tom Cotton, author of the recent open letter to Iran, tells ABC. Meanwhile, Democrat Rep. Adam Schiff says, "The last thing we want is for the international community to think that we came this close to a negotiated end to Iran's nuclear program and the United States Congress got in the way."