It took a year of tortuous talks and painful compromise for Russia and the United States to forge their strategic nuclear arms cut treaty. That may prove child's play compared with the next step toward nuclear disarmament. The New START treaty, signed by presidents Barack Obama and Dmitry Medvedev last April and set to be put into force at a ceremony in Munich on Saturday, is the centrepiece of a "reset" in long-strained bilateral relations as well as a crucial springboard towards a world without nuclear weapons.
But that finish line lies beyond a minefield of obstacles - from lingering fears of nuclear domination to domestic politics and the devilish complexities of doing away with weapons that have never before been the subject of negotiations. "Moving to the next round will not be easy at all," said Fyodor Lukyanov, editor of the journal Russia in Global Affairs.
New START, which lowers the ceilings on stocks of long-range weapons, will enter force when Russian Foreign Minister Sergei Lavrov and US Secretary of State Hillary Clinton exchange ratification documents during a security conference in Munich. The former Cold War foes have already signalled differences over further cuts in the world's largest nuclear arsenals. The first hurdle looms this year over an armament that is not restricted by New START: tactical nuclear weapons.
The towering Intercontinental ballistic missiles (ICBMs) that that are restricted by the treaty are icons of the Cold War - the stuff of public displays of military might and private nightmares of nuclear armageddon. But cutting tactical nuclear weapons, with ranges up to 500 km (300 miles) - a fraction of the 5,500 km (3,400 miles) and more that strategic missiles can travel - could be a stiffer challenge for two countries that have not even revealed the numbers in their possession.
When the US Senate ratified New START, it ordered Obama to seek negotiations on tactical nuclear weapons within a year after it enters into force. Not so fast, says Russia, whose stockpile is several times larger than that of the United States - compensation, in Moscow's view, for the relative weakness of its conventional forces. Moscow says talks should not be held until each country confines its tactical nuclear weapons to its own territory.
Translation: Russia can keep warheads on European territory - its own - while the United States must withdraw the few hundred tactical nuclear weapons it is estimated to maintain in allied Nato countries on the continent. That's not necessarily a deal-killer. The United States has already removed most of the more than 7,000 tactical nuclear warheads it deployed in Europe at the height of the Cold War, and some Europeans are urging a complete withdrawal.
The United States, meanwhile, has something that could sweeten a deal for the Kremlin to cut tactical nuclear weapons: a couple thousand strategic nuclear warheads that are not restricted by New START as long as they are not deployed. Arms control experts say a solution could be an umbrella treaty that would set ceilings on all US and Russian nuclear weapons - tactical and strategic, deployed and undeployed. "This will be a completely new kind of negotiation, if it does take place," Lukyanov said.
There is a welter of other factors that could hinder progress toward a new treaty. One major complication comes from concerns about other nuclear-armed nations - chiefly Britain, France and China - whose smaller arsenals will become increasingly significant as Russia and the United States make deeper cuts. These smaller arsenals must be included sooner or later for a nuclear-free world, which would mark a milestone for disarmament but likely make agreements even more elusive.