An agreement between the United States and Russia to slash their nuclear arsenals was in danger of collapse after an influential Republican senator in the US said it should not be voted on this year.
With his statement on Tuesday, Senator Jon Kyl from Arizona dealt a major setback to Barack Obama's efforts to improve ties with Russia and to his broader strategy for reducing nuclear arms worldwide.
The treaty, known as New START (Strategic Arms Reduction Treaty), had been seen as one of Obama's top foreign policy accomplishments.
Without the support of Kyl, the leading Republican voice on the treaty, Democrats have little hope of securing at least eight Republican votes - the minimum they would need for ratification in the current Senate.
Kyl's position, unless reversed, would delay the vote until the newly elected Senate, with an expanded Republican minority, has been sworn in in January. Democrats would then need the support of at least 14 Republicans.
The White House has been trying to avoid that fate, knowing that ratification could slip out of reach in the face of opposition to the treaty from most Republicans and an increasingly partisan political environment in Washington.
At a minimum, that probably would set the treaty back for months, because Republicans are likely to demand new hearings in the Senate Foreign Relations Committee so that newly elected lawmakers would be briefed.
Following Tuesday's setback, Joe Biden, the vice president, warned that failure to approve the treaty this year would endanger national security. He pointed out that the treaty would renew US authority that expired last year to inspect Russia's nuclear arsenal.
Senate Democrats were holding out hope. John Kerry, the Chairman of the Senate Foreign Relations Committee and a Democrat, said he had discussed the issue with Kyl on Tuesday and believed the door was still open to a vote before the end of the year.
"Ratifying New START is not a political choice, it's a national security imperative," he said.
Early resolution unlikely
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Kyl's statement, however, appeared to leave little room to resolve the issue quickly. He said he told Harry Reid, the Senate majority leader, that he did not believe the treaty could be considered this year.
The treaty would reduce US and Russian limits on strategic warheads to 1,550 for each country from the current ceiling of 2,200. It also would set up new procedures to allow both countries to inspect each other's arsenals to verify compliance.
Republicans have argued that the treaty would limit US missile defense options and does not provide adequate procedures to verify that Russia is living up to its terms.
Kyl has argued that it makes no sense to reduce the number of US warheads until more is done to maintain and modernise the remaining arsenal.
Obama has made ratification of the treaty one of his top priorities for the remaining weeks of the current Congress. He reassured Medvedev on Sunday that he was committed to getting Senate approval for the accord by the end of the year.
Democrats fear the treaty will face greater opposition when the new Congress is seated next year because losses in recent nationwide elections left them with only a slim majority in the Senate.
Kyl's statement prompted the administration to initiate a round of consultations with the senator, followed by a statement from Biden.
Without ratification of this treaty, we will have no Americans on the ground to inspect Russia's nuclear activities, no verification regime to track Russia's strategic nuclear arsenal [...] and no verified nuclear reductions," Biden said.
'US arms to stay'
Meanwhile, the British newspaper Guardian reported a earlier proposed plan to withdraw US nuclear weapons from Europe has been omitted from Nato's draft strategic doctrine, due to be adopted by a summit this weekend in Lisbon.
In draft of the alliance's "new strategic concept, seen by Guardian, nuclear weapons remain at the core of Nato doctrine, and an attempt to withdraw an estimated 200 US nuclear bombs from Europe is not mentioned".
Germany, the Netherlands and Belgium had pushed to have the tactical weapons removed, with the encouragement of supporters of disarmament in the Obama camp including Ivo Daalder, the US ambassador to Nato.