The landmark 1991 arms control treaty negotiated by President George H.W. Bush and Soviet leader Mikhail Gorbachev that brought the Cold War nuclear arms race to an end expires Friday night.
U.S. and Russian negotiators have been working round-the-clock in Geneva to replace the Strategic Arms Reduction Treaty, or START, and maintain some of its key provisions, but that work is not yet completed. Both governments say they will abide by the terms of the treaty as the deadline passes.
For months, U.S. and Russian officials have been negotiating a replacement for the START, especially some way to extend key verification measures that have allowed each side to maintain a timely and accurate accounting of the strategic nuclear weapons the other side has deployed.
The START called for the reduction of each side's deployed strategic nuclear arsenal on long-range bombers, missiles and submarines to about 6,000. Those targets were reached years ago, and now the United States and Russia each deploy fewer than 2,000 strategic nuclear warheads.
Maintaining the verification measures of the START is important to the Obama administration. It was on the agenda Friday when Secretary of State Hillary Clinton met with her Russian counterpart, Sergei Lavrov, in Brussels.
"We always knew this would be very difficult. Remember, the prior administration didn't believe in arms control treaties, and so we were pretty much starting from scratch, and these are highly complex technical negotiations," Clinton said.
In 2002, the George W. Bush administration signed the Moscow Treaty that brought the nuclear arsenal of both sides down to current levels.
But President Obama has mapped out far more ambitious goals for the reduction of nuclear weapons. Clinton explained the rationale for this in a speech on arms control in October.
"Clinging to nuclear weapons in excess of our security needs does not make the United States safer. And the nuclear status quo is neither desirable nor sustainable. It gives other countries the motivation — or the excuse — to pursue their own nuclear option," she said.
Russia and the United States have already agreed to new levels for nuclear weapons — roughly 1,600. That turns out to have been the easy part.
Achieving reciprocal verification has been one of the hard parts. The U.S. stopped making long-range missiles years ago, and Russian personnel who monitored that production in the U.S. returned home. But Russia continues to produce long-range missiles, at a facility at Votkinsk on the Volga River, about 800 miles east of Moscow.
With the expiration of the START, American monitors at Votkinsk were set to leave. Arms control experts argue that even though the United States and Russia are no longer enemies or adversaries, verification measures such as this are still very important.
In fact, the fewer the nuclear weapons, the more verification matters, according to Joseph Cirincione, president of the Ploughshares Fund, a nonprofit group that seeks to reduce nuclear weapons worldwide.
"Once you start going down to, say, a thousand or a few hundred deployed weapons, then it really starts to matter. You want to be sure that you can account for those weapons, that there's no secret stock of weapons that the other side is using, that there's no breakout capability where one side could suddenly double or triple the number of weapons they have," Cirincione says.
The possibility of miscalculation is another good reason to maintain verification measures, says Jeffrey Lewis, who runs the Web site armscontrolwonk.com.
"We do constantly see on the Russian side and on the American side ridiculous over-estimates of each other. ... The Russians think the United States is 10 feet tall, and sometimes we think the same thing about them," Lewis says.
There are other issues that still divide the U.S. and Russia — for instance, disagreements over how deployed nuclear warheads and their delivery systems are counted. Russia wants to include missile defenses. The U.S. does not.
Despite the expiration of the START, it looks like the United States and Russia will continue working on these issues. Any new treaty will have to be ratified by the U.S. Senate and the Russian Duma.