Odds of nuclear attack in U.S. at 50% next 10 yrs?

On Nov. 4, Remember 9/11, (New York Times)…Jeffrey Goldberg

The next president must do one thing, and one thing only, if he is to be judged a success: He must prevent Al Qaeda, or a Qaeda imitator, from gaining control of a nuclear device and detonating it in America.

Many proliferation experts I have spoken to judge the chance of such a detonation to be as high as 50 percent in the next 10 years. I am an optimist, so I put the chance at 10 percent to 20 percent.