The scientists take heart in the fact that Obama has said he intends to "make the goal of eliminating all nuclear weapons a central element in [U.S.] nuclear policy."
That's in stark contrast to the premature claim of victory by President Bush in 2004, who proclaimed "We busted the A.Q. Khan network" after Kahn, a Pakistani physicist, confessed to supplying nuclear weapons technology to Libya, Iran and North Korea.
Kahn was later pardoned by Parvez Musharraf, president of Pakistan. Many of those who assisted in Kahn's exploits either slipped through legal loopholes or served very short sentences, according to researchers at the Monterey Institute of International Studies' Center for Nonproliferation Studies.
It is not known exactly how much of a role Kahn played in North Korea's ability to set off a low yield test explosion in October 2006. The fact that the weak explosion was detected by the International Monitoring System is one of the few bright sides to this story.
That means no one is likely to join the nuclear club unannounced.
So, where is the greatest threat today? It's not likely that a band of terrorists, no matter how well funded, will build a nuclear weapon in a cave somewhere in the Middle East. It's not that easy.
And it's hard to imagine that any country would will its own destruction by nuking another nuclear power. But it doesn't take much to imagine suicide bombers with nuclear weapons bringing a nation, and perhaps the world, to its knees.
But where would they get such a weapon?
"The most direct way for terrorists to acquire a usable nuclear weapons capability would be through theft, or illegal purchase, and the danger is real," Drell and James Goodby, also of the Hoover Institution, warned in 2004. The activities of Pakistan's Kahn, who has since recanted his confession, are not reassuring.
So the most likely scenario is this: terrorists somehow acquire a nuclear weapon from a member nation of the nuclear club, which is growing in membership, and manage to somehow place it in a strategic location and set it off. It wouldn't be easy, but few thought it would be easy to wipe out New York's twin towers until 19 men pulled it off.
So where do we go from here? Drell has two suggestions.
"Rekindling the vision of Reykjavik will be President Obama's main challenge, but realizing that goal will be very difficult," he said. The second goal is to convince the rest of us that it's really possible to solve this difficult, and potentially catastrophic, problem.
In the meantime, the "Doomsday Clock" at the Bulletin of Atomic Scientists, founded 60 years ago by scientists at the Manhattan Project, is ticking away.
The hands of the clock have been moved 19 times, an iconic symbol of changing global uncertainties. The clock was initially set at seven minutes to midnight in 1947. They were moved to two minutes before midnight in 1953 after the United States decided to build the hydrogen bomb.
The world looked safer in 1991, with the Cold War officially over, and the hands were set to 17 minutes before midnight.
The hands were reset on Jan. 17, 2007, as more nations moved closer to joining the nuclear club. Today, the hands are set on five minutes to midnight.