Negotiations over a new arms control treaty between the US and Russia resumed in Geneva today amid growing criticism of Barack Obama's conciliatory policy towards the Kremlin from human rights groups and a newly emboldened Republican party.

Obama and Russia's president, Dmitry Medvedev, indicated last week that a successor agreement to the Strategic Arms Reduction Treaty (Start 1) could be signed within weeks. The 1972 treaty expired on 5 December, leaving Moscow and Washington without an operational arms control regime for the first time in 40 years.

A spokesman for the US mission in Geneva, Michael Parmly, said today that the delegation hoped "the remaining negotiations can be concluded quickly," but declined to say when that might be.

But even if the sides manage to resolve their outstanding differences over verification and missile defence, serious doubts remain about Obama's ability to ratify any new treaty ahead of November's mid-term US elections. Analysts say that if Obama fails to persuade the Senate to back a deal, the current arms control "vacuum" may continue.

Sixty-seven votes are needed in the Senate to ratify the treaty, and the Republican Scott Brown's victory in the Massachusetts Senate race last week compounded Obama's difficulties, emboldening the opposition and creating anxiety among centrist Democrats. When the treaty comes up for consideration, Republicans will be inclined to portray Obama as making concessions on defence.

"They don't want President Obama to score a major policy victory that would lend heft to his credentials as a great American statesman in the run-up to the midterm elections," said a US official familiar with the treaty talks. "They are going to use this as a political football and play this in a political way rather than out of consideration for its merits."

A year after his inauguration, critics claim Obama has failed to realise many of his major foreign policy goals, including on Iran and the Middle East, with his "reset" strategy towards Russia yet to produce tangible results. One of Obama's key aspirations was to improve relations with Moscow in return for closer co-operation on Iran and its nuclear programme and the war in Afghanistan.

So far, however, the Kremlin has made no significant concessions towards the Obama White House, either over a sanctions regime against Tehran or anything else. Obama's decision to dump the Bush-era missile defence shield in central Europe last summer – an issue that had enraged Vladimir Putin, Russia's hawkish prime minister – failed to elicit any reciprocal gesture from the Russian side.

Obama's tactical silence on human rights issues in Russia and other repressive former Soviet republics, meanwhile, has infuriated human rights defenders. During a visit to Moscow last December, the US secretary of state, Hillary Clinton, made clear that human rights issues would now be discussed "behind closed doors" with the Russian government, prompting accusations that Obama had relegated values to third-tier status.

"I don't think keeping silent is the way to go. At this stage, I would express disappointment with the Obama-Clinton approach," Allison Gill, the director of the Russia office of Human Rights Watch, said. "I don't think there is any evidence that pragmatic silence has proved particularly effective, certainly in promoting human rights."

Russian human rights defenders concur. "A more definite approach from the Americans wouldn't hurt civil society in Russia. You have to speak the truth," Lev Ponomarev, a prominent activist who has met Clinton, said. Ponomarev complained Clinton had not offered any criticism of the situation in Russia, where journalists are routinely murdered, and said the secretary of state's short encounter with civil society representatives had been a "protocol" one.

Some believe that in its eagerness to improve relations with Moscow, the Obama administration made key mistakes, in particular in its erroneously "optimistic" assessment of Medvedev. During his visit to Moscow last July, Obama held long face-to-face negotiations with Medvedev while snubbing Putin, in an unsubtle attempt to boost Medvedev's domestic prestige.

Since then, however, it has become clear that Medvedev is not the liberal reformer that some had hoped but part of Russia's managed democracy construct, in which elections are stage-managed and dissent swiftly squashed. Few are in any doubt that it is Putin who continues to run the country, and who remains the supreme arbiter of both domestic and foreign affairs.

"I think the administration had the feeling that more had changed in the Russian political scene with the arrival of Medvedev than was actually the case," Sam Greene, deputy director of the Moscow Carnegie Centre, said. Asked whether the Obama administration had been naive in its assessment, he said: "I think they were very quickly disavowed of the notion [that Medvedev was a liberal] – during the summit itself, in fact."

A new Start treaty would face an uphill battle to win Senate approval, he added. "The reality is that in a hard-fought election, anything can become hostage with politics. I think the state department and the administration will be wary of risking a treaty as important as this in a political season as fraught as we are likely to see towards the summer and fall." He went on: "If they don't get a treaty soon, it may have to wait until next year to ratify."

James Collins, former US ambassador to Russia under Bill Clinton, said ratification entirely depended on whether it was consistent with the US military's nuclear posture review, currently under way, and the military's and the intelligence community's approval of its verification mechanisms.

He said the time was ripe for the eventual treaty language to be judged on its own merits, with few available political "cheap shots".

"It has been negotiated to serve American interests. Nobody was playing politics or games with it. We didn't have artificial deadlines, and it wasn't set against Obama's Nobel prize," Collins said.

Over the last month, the Republicans have considerably stepped up their attack on Obama's Russia strategy, directing their fire in particular at Vladislav Surkov, the Kremlin's chief ideologue. Surkov is synonymous with the rollback of democracy during the Putin era. He visited Washington last week as co-chair of a new US-Russian intergovernmental civil society working group set up by Obama and Medvedev.

On 11 December, more than 60 Republican members of Congress signed a letter urging Obama to boycott the meeting until Surkov, Medvedev's deputy chief of staff, was replaced by "someone who has not been involved in establishing oppressive and undemocratic policies". They also expressed concern over Russia's human rights record.

In an interview with Radio Liberty, Michael McFaul, special assistant to Obama and senior director for Russian affairs at the National Security Council, played down the "controversy" over Surkov.

He said it was better to engage with Russia, even if there were "disagreements", than to "sit in our cubbyholes and not have any real connectivity with those that we think we are disagreeing with".

Some believe Obama has brought about a marked improvement in US-Russian relations – at least in tone. "There have been positive steps. It isn't a shouting match any more," Sergei Rogov, the director of Moscow's Insitute for US and Canada Studies, said. Rogov acknowledged there were disagreements – over Russia's claim, for example, it is entitled to a sphere of influence in post-Soviet countries. He also noted that trade and investment were "going down".

The key test, he said, was whether Obama could deliver a new Start treaty. "If we sign the treaty, there may be more progress in other areas; if we don't sign, we will have a repetition of the old story – a nice declaration but no practical achievements."

Others said Obama's failure to reap any dividends from his rapprochement with Russia was due to a more profound conceptual weakness: his failure to define America's role in the 21st century. "The problem is Obama's foreign policy. He is trying to solve complex problems without having a clear strategy of how to position the US in the new world," Fyodor Lukyanov, editor-in-chief of Russian in Global Affairs, said.

Start 1 was approved in 1992 on a 93-6 vote. Despite the acrimonious climate in Washington, some analysts hold out hope the new treaty will not get bogged down in domestic electoral politics, and will be judged on its own merits.

"The concerns about US defence go beyond the party-line divisions," said Ariel Cohen, a Russia and Eurasia analyst at the conservative Heritage Foundation. "In the past, both Republicans and Democrats were those who approved. And in things like nuclear weapons, responsible politicians do not trifle."