On the eve of a landmark nuclear deal with Iran, President Obama's Democratic allies in Congress are worrying over a peripheral issue that, if included, could hamper support for it.
Democrats are grappling with a reported phased lifting of a United Nations arms embargo, which the Iranians have demanded as the international community looks to lift sanctions worth some $150 billion. In exchange, Iran would reduce its centrifuges, convert a once-secret, underground mountain facility to one used only for peaceful purposes, and increase access for international inspectors to all of its nuclear facilities, among other points described in the White House's framework struck in April.
"My concerns would be the same that anybody would have, which is a concern of a proliferation of weapons in that region by the Iranians," said Sen. Michael Bennet of Colorado, adding that the embargo concerning conventional arms "is not what this negotiation is about."
On Monday, Sen. Robert Casey of Pennsylvania said the issue was "of great concern" to him, Sen. Christopher Coons of Delaware reiterated his opposition, and Sen. Richard Blumenthal of Connecticut said it "probably" would be a line he couldn't cross.
And Sen. Robert Menendez of New Jersey, among the Democrats most skeptical of the talks, said he couldn't support the deal if it relaxed the embargo as it would allow Russia, a negotiating partner, to sell Iran an advanced air-defense system.
"Listen, the last thing we need to do is give Iran the ability to have the wherewithal to have arms going throughout the region," he said. "They're already involved in Yemen, in Syria, in Lebanon, in Iraq. "¦ What is lost here is that if we lift the arms embargo, then the Russians freely can sell the S-300 [missile] to them, and that makes it a lot more difficult in the future—should Iran violate the agreement and move towards their nuclear capability for a nuclear weapon—of trying to strike them with the S-300 as a defense missile system. For all of those reasons, it should be a redline. And the intercontinental missile issue should also be a redline."
Democrats' opposition follows in the footsteps of top members of the administration, including outgoing Joint Chiefs Chairman Martin Dempsey and Defense Secretary Ashton Carter, who explained their views last week in a Senate Armed Services hearing. "The reason that we want to stop Iran from having an ICBM program is that the I in ICBM stands for intercontinental, which means having the capability from flying from Iran to the United States," said Carter. "And we don't want that."
"Under no circumstances should we relieve pressure on Iran relative to ballistic capabilities and arms trafficking," added Dempsey.
Republicans, who have criticized the administration's Iran strategy since before the Joint Plan of Action interim agreement of November 2013, have added it to their litany of concerns.
"There was a huge shift when under JPOA we went from dismantling their program to acknowledging enrichment," Senate Foreign Relations Committee Chairman Bob Corker said. "That was a pretty big shock to folks. And then from then on it's gotten—you know the anytime, anywhere inspections—where's that going to end up? They're saying military sites are off. Now the arms embargo seems to be coming in. I don't think anybody can say it's been going in a more positive way, OK?
"I mean, so many redlines have been crossed," he added.
Should a deal be struck Tuesday after several deadlines have been broken—Corker said Monday night that he suspected it would come within 36 hours—Congress will have 60 days to review and potentially vote on it. A veto-proof, two-thirds majority would be necessary to continue congressional sanctions, which would imperil the carefully calibrated agreement set by Iran and the six major global powers, including the United States. That's a very tall task, but the reports of the arms-embargo provision have Democrats worried and all members underscoring the potentially historic nature of a deal more than 18 months in the making.
"This is one of the most important international agreements that the United States has ever entered into," said Sen. Susan Collins of Maine. "It has ramifications not only for the stability of the region but for our national security as well. And it's important that we get this right."
Rachel Roubein contributed to this article
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Alex Rogers covers Congress as a staff correspondent for National Journal. He previously worked as a political reporter at TIME. He is a native of Bethesda, Maryland and a graduate of Vanderbilt University.