With Russia's 65th Victory Day parade in full swing (and a grande one it is), and Gazprom looming over Ukraine's very independence, it may be hard to think that the US and the Russians are putting together a working relationship. But on the issue of nuclear weapons, the two states may have actually achieved a deeper understanding.
Of course, the two states will continue to be rivals as far as spheres of influence--of this there is no doubt. But, ultimately, there is common ground on the issue of nuclear proliferation, and the two states are taking advantage of this.
The common ground is such: Neither state wants nuclear arms to fall into the wrong hands. At the end of the day, it is much better for both Russia & the US that there are a limited number of nuclear-armed states. This both gives the Nuclear Club a strong bargaining upper-hand with other nations, and reduces the risk of arms ending up in the hands of (undeterrable) terrorist groups. Both states furthermore have sufficient retaliatory capacity that few minor changes (like # of warheads) can significantly impact.
Where are we seeing this cooperation play out? A number of recent events, not yet explicitly linked together by either state's spokespeople, suggest a wider cooperation afoot:
1) SMART. The renewed nuclear treaty really allows both countries to get rid of their older, obsolete arms easily. Fewer, more advanced arms allow both countries to save a bit on maintenance costs, but more importantly, help both countries keep track of their weapons (remember the 2007 incident a few years where a US [CORRECTION:]B-52 mistakenly flew with weapons? Russia is not the only state for whom it is difficult to keep track of them all). Beyond that, it's symbolic, but it shows both states are willing to put time into cooperating on the issue, even with many other competitive games underway.
2) Pressure on Iran. Russia and China look to be in favor of some limited forms of sanctions against Iran (not including, for example, a gasoline ban). While the sanctions themselves are unlikely to be crippling, Iran's loss of Russia & China's support on the issue would be. Iran is China's second-largest oil supplier--China's willingness to risk relations with Iran in order to keep it in line on the nuclear issue would be significant. But, ultimately, Russia & China don't want a nuclear-armed Iran, either. Russia would enjoy Iran's continued existence as a nuisance to the United States, but no more than that. Iran's possession of nuclear weapons would make it a threat to Russia and China's interests--not necessarily a nuclear strike (hitting either Russia or China would be suicidal); but it would grow increasingly daring and audacious in its region. China and Russia would certainly prefer to dominate the areas to the east and north of Iran themselves.
But if the US has won over the Russian and Chinese hands towards pressuring Iran to dismantle its nuclear program, the odds of its failure increase dramatically (namely, Ahmedinejad is likely to lose sufficient domestic support to press it forward if Iran loses its key allies over the issue). It may be the only option the US has to stop the program that doesn't include war.
3) BMD. We see also Bulgarian and Czech involvement in the American BMD (Ballistic Missile Defense) system. The Czechs have confirmed their own plans to place radar and missile systems within their borders; Bulgaria has made its intentions clear that they desire to be a part of the system as well. Such moves come amid the United States backing off pressure in Ukraine (where it has all but conceded the loss of Ukrainian autonomy in the near-term) and failing to counter Russian sympathy diplomacy in Poland. Some of this is the United States being, frankly, outmaneuvered by a truly brilliant Russian foreign policy.
But some of it appears to be a very quite understanding of spheres & values. The Russians are distinctly not making a fuss over the Bulgarian and Czech missile defense systems, where Polish plans for the very same thing were met with military officials murmuring of nuclear war (and not facing reprimand afterward). Russia & the United States may, for now, be deciding that they have more pressing issues to tackle than each other (as much as I may personally disagree with said policy).
The suggestion to be made is that an understanding of sorts may have emerged. Perhaps it is part of a larger deal, where the two sides have found room to concede on issues of less import to secure cooperation on issues of greater import. The opposition opinion is that Obama is being distracted by nuclear arms negotiations when there are more important areas to burn his time and political capital. But at the end of the day, the United States is simply not in a position to counter Russian expansion into Ukraine, Georgia, and certainly not Central Asia. Furthermore, the balance of interest is far in Russia's side--if Russia loses any of these 3 regions (especially Ukraine), it is in danger of being permanently marginalized. These areas aren't areas where the US is ready to fight and win--this unfortunate reality may be what's driving America's current deal-making (rather than conflict-making) strategy with Russia.