Vienna: President Obama and Iranian Supreme Leader Ayatollah Ali Khamenei have one thing in common: Both have voiced doubts that nuclear talks will produce a deal to curtail Iran’s nuclear programme.

That’s only in part because negotiators need to hack through a thicket of technical and political issues to close the distance between the two sides’ opening positions. It’s also because some of the most important negotiations will be on the home fronts in Tehran and Washington.

Hardliners in Iran are pressing President Hassan Rouhani to reject dismantling any part of his country’s nuclear infrastructure. In the US in a congressional election year, some lawmakers and lobbying groups — backed by American ally Israel — urge Obama to accept nothing less than elimination of virtually all Iranian nuclear activities, as well as intrusive inspections to ensure that the Islamic Republic can’t secretly develop a nuclear weapons capability.

The Obama administration has ambitious objectives for curtailing Iran’s programme, and that’s “not merely for show,” said Suzanne Maloney, an Iran specialist at the Brookings Institution, a Washington policy research organisation. Given the pressure from Capitol Hill and Israel, sticking with a tough position is “what the traffic will bear in this town,” she said.

Obama has said publicly that the odds are no better than 50-50 that an interim accord now in effect will lead to a lasting agreement allowing Iran a limited nuclear enrichment programme with sufficient safeguards to satisfy Israel, the US and the world. Even so, Obama says diplomacy remains the best means to prevent Iran from acquiring a nuclear weapon.

Khamenei, who insists that Iran’s programme is peaceful, said on Monday he’s “not an optimist” about the talks that his president and foreign minister have championed as a path to removing the sanctions that have hobbled Iran’s economy.

Reaching a comprehensive deal “is challenging but not impossible,” Iran’s Deputy Foreign Minister Abbas Araghchi said in an interview last night in Vienna.

One difficulty that’s dogged negotiations between Iran and six world powers — the US, Britain, France, Germany, Russia and China — since they began in October is rhetoric by hardliners in Tehran and Washington who oppose compromise and accuse their leaders of giving up too much in the first-step agreement signed November 24 that freezes much of Iran’s sensitive nuclear work in exchange for limited relief from certain sanctions.

That’s forced the US and Iranian governments to deny conceding anything and to issue tough statements. “Then the other side reacts, creating an echo chamber” of maximalist positions, said Daryl Kimball, executive director of the Arms Control Association in Washington.

What really matters, said one US official involved in the Vienna talks who spoke on condition of anonymity, isn’t what’s said in speeches, but what’s said behind closed doors, and the purpose of this week’s talks is to lay out the essential issues and both sides’ red lines.

With congressional elections looming in which Obama needs as many Democratic seats as possible to protect his health-care law and other domestic priorities, support for tough sanctions on Iran has been a rare bipartisan issue on Capitol Hill since 2011.

So far this year, the Senate Democratic leadership has held off on a new sanctions bill that Obama has threatened to veto, saying it would derail diplomacy and make a risky military strike on Iran’s nuclear facilities more likely.

“With midterm elections coming up, pressure will intensify for strong measures in Congress” once the interim deal expires in July, Maloney predicted, bringing with it the risk of “a train wreck” if new sanctions come to a vote before a final agreement is negotiated with Iran.

Imposing new US sanctions at this stage would isolate the US from its five negotiating partners, increase the probability of war and undermine the new Iranian president’s efforts at diplomacy, according to a report being released Tuesday by the Iran Project, a group dedicated to improving relations between the US and Iran. Signatories to the report include former US Undersecretary of State Thomas Pickering and former Central Intelligence Agency official Paul Pillar.

Retired Lieutenant General Robert Gard, chairman of the Centre for Arms Control and Non-Proliferation, said he’s concerned about possible efforts in Congress to develop a nonbinding resolution specifying what members would endorse in an agreement with Iran and what they would reject.

What’s often overlooked in all the talk about the US and Iranian positions, “is that there are six countries negotiating with Iran, not just the US,” he said. While “we have been able surprisingly to get the Chinese and Russians to go along with stringent sanctions so far,” if Congress took actions that prompted the Iranians to walk away, blame would fall on the US, according to Gard.

The Obama administration has made decisions over Iran’s nuclear programme based on national security interests, not on domestic politics, said a second US official involved in the talks. Were domestic elections the guiding principle, the administration wouldn’t have worked so hard against Democrats as well as Republicans to hold off new sanctions during the six- month interim deal, said the official, who also spoke on condition of anonymity because of the sensitivity of the talks.

A third administration official, who also asked not to be identified for the same reason, disputed the view that the Iran talks will have much influence on this year’s midterm elections. Iran isn’t a major issue in key Senate races such as those in Alaska, Arkansas and Louisiana, the official said. The leading sponsors of a bill to impose new sanctions — Senators Bob Menendez, Democrat-New Jersey, and Mark Kirk, Republican-Illinois — aren’t up for re-election this year.

Any agreement that left Iran with the capacity to quickly produce significant amounts of weapons-grade material would be opposed by many in Congress, who probably would try to pass legislation to overturn it, said Gary Samore, Obama’s former chief non-proliferation adviser.

Samore, now a researcher at Harvard University and president of the New York-based group United Against Nuclear Iran, said he also sees no indication that Obama is prepared to accept a weak deal.

Much will hinge on carefully chosen wording that both sides can agree on. “Iranians need to be able to walk away from any final deal able to say that they have preserved their ‘nuclear rights,’ as a well as a substantial amount of their infrastructure,” Maloney said in an interview. “There’s going to a lot of finessing.”

Peter Galbraith, a former US and United Nations diplomat who spent 14 years as a staff member on the Senate Foreign Relations Committee, said the “levers” Congress has to dictate the outcome are relatively limited, and he doubts the elections will cause Democrats or the president to adopt hard-line positions that derail talks.

“This is not what voters are concerned about, and many believe it is worth giving diplomacy a chance,” said Galbraith.

Some in Washington cite public opinion polls that show Americans are tired of war after the conflicts in Iraq and Afghanistan, suggesting that the elections might push Congress away from hawkish positions.

“If the debate over Syria is an indicator, the winning card in the congressional races may very well be how lawmakers kept the US out of another war,” said Trita Parsi, president of the National Iranian-American Council, an advocacy group for Americans of Iranian descent.