VIENNA – Negotiations with Iran come to an ostensible end next week, assuming the world’s top diplomats, gathered in Vienna to demonstrate their skills as brinksmen and brokers, agree that talks over the Islamic Republic’s nuclear program have proven futile.Should the diplomatic effort here reach the self-imposed deadline of July 20 without a comprehensive agreement, the immediate task of those at the table will be to identify which party is primarily to blame. Indeed, that separate effort has already begun.US officials say that Iran is now insisting on attaining a uranium enrichment capacity well beyond the current infrastructure of its existing nuclear program – meaning Iran proposes to expand, not reduce, its ability to produce nuclear weapons material, and to degrade, not reinforce, the trust of the international community in its efforts to pursue peaceful nuclear energy.That is only one in a series of “unworkable and inadequate” positions still held by the Iranians, mere days before the expiration of talks and six months after they began, claim the Americans.Leadership in Congress had predicted this moment would come to pass. Across party lines, in both the upper and lower house, lawmakers have told the Obama administration they stand at the ready to pass harsh new sanctions legislation should diplomacy fail.Such a bill – proposed twice already by Democrats – would be easier to pass through Congress than a Mother’s Day resolution.The real challenge within the US position is the same carrot and stick that all parties credit for dragging Iran to the table in the first place: bills already codified into law sanctioning the Islamic state that will require US legislative action to ease, lift, suspend, or repeal should a deal be reached.Iran has requested a provision be included in the text of a comprehensive joint plan of action that explicitly requires legislative action – a commitment US President Barack Obama, or any president, would be adventurous to make.That proposal, furthermore, has come from a delegation led by Iranian Foreign Minister Mohammad Javad Zarif, who has lived in the United States and knows full well the dynamics, politics, and limitations of a structurally fractured Congress.When experts suggest a majority of sanctions can legally be set aside, in one way or another, by the president’s executive waiver authority, US diplomats question the motivation of such a position from Tehran, as talks reach a turning point.But Iranian negotiators say they cannot agree to a long-term reduction in their capacity based on the word of a sitting president with less than three years left in office.Last week, 344 members of the House sent Obama a letter calling for better communication on the nuclear issue – and reminding the White House that the bills they have passed, four in the last five years, do not separate sanctions against Iran’s nuclear program from its support for global terrorism, human rights abuses, and ballistic missile research and development.The message: Congress will struggle to lift sanctions against Iran, even if the president takes the unexpected step of asking the body to do so.“To say that there is not one single sanction that can be lifted in the context of a nuclear agreement, of course, is not a plausible position,” one senior Obama administration official said on Saturday, questioned by The Jerusalem Post. “Equally true is to say that all sanctions get lifted in the context of a nuclear agreement is not plausible because there are... terrorism and human rights-related sanctions that are quite specifically targeted at other behavior of Iran.”“Ultimately, “ the official continued, “this is going to be a negotiation within these talks, and then consultation with Congress to determine what are effectively nuclear-related sanctions and what are not. “ Complicating the matter are midterm elections only four months away. Republicans have a strong chance at reclaiming control of the Senate and, from their first day, dictating votes on all matters, Iran sanctions included.The politics of the task in Washington, publicly aired so close to the deadline, also put daylight between the United States and its partners at the table in the European Union, represented in Vienna by EU High Representative Catherine Ashton, the union’s highest-ranking foreign minister.Ashton’s spokesman, Michael Mann, told the Post that he cannot speak to US law; but that the EU had successfully sanctioned Iran’s nuclear program, and its financiers, separate and apart from its sanctions on Iran’s human rights violators.“There are specific European Union nuclear-related sanctions, and [Ashton] is negotiating on the nuclear issue ,” Mann said. “ Both sides have fully respected the Joint Plan of Action, and we would hope and assume that, if an agreement was reached here, then both sides would be able to fully respect that as well. “ Thus, at a juncture US Secretary of State John Kerry has called “critical” in a long saga with Iran over its pursuit of nuclear power, the primary weapon used by Western governments to compel Iran to change course might now be used to drive a wedge in the text of a final deal.That, of course, coupled with other “very significant gaps,” according to the US officials.“ There’s a real danger that the Iranians, at the last moment, will make a proposal that seems reasonable to the Russians and the Chinese, but completely insufficient to France, England, and Germany, and therefore puts the onus on the United States as the intransigent party,” said Matthew Bunn, a professor at the Belfer Center for Science and International Affairs at Harvard University.“The US might have to work quite hard on coalition unity to avoid that.”Should world powers and Iran agree that progress has been made, their negotiations may be extended from July 20 by up to six months.