Stealing some 100 pounds of bomb fuel would require help from rogue individuals inside some government who are prepared to jeopardize their own lives. The terrorists, notes Mueller, would then have to spirit it "hundreds of miles out of the country over unfamiliar terrain, and probably while being pursued by security forces."
Then comes the task of building a bomb. It's not something you can gin up with spare parts and power tools in your garage. It requires millions of dollars, a safe haven and advanced equipment -- plus people with specialized skills, lots of time and a willingness to die for the cause. And if al-Qaida could make a prototype, another obstacle would emerge: There is no guarantee it would work, and there is no way to test it.
Assuming the jihadists vault over those Himalayas, they would have to deliver the weapon onto American soil. Sure, drug smugglers bring in contraband all the time - but seeking their help would confront the plotters with possible exposure or extortion. This, like every other step in the entire process, means expanding the circle of people who know what's going on, multiplying the chance someone will blab, back out or screw up.
Mueller recalls that after the Irish Republican Army failed in an attempt to blow up British Prime Minister Margaret Thatcher, it said, "We only have to be lucky once. You will have to be lucky always." Al-Qaida, he says, faces a very different challenge: For it to carry out a nuclear attack, everything has to go right. For us to escape, only one thing has to go wrong.
That has heartening implications. If al-Qaida embarks on the project, it has only a minuscule chance of seeing it bear fruit. Given the formidable odds, it probably won't bother.
None of this means we should stop trying to minimize the risk by securing nuclear stockpiles, monitoring terrorist communications and improving port screening. But it offers good reason to think that in this war, it appears, the worst eventuality is one that will never happen.