Yeah, well who isn't? There are probably sixty nations and ten thousand independent groups who would love to carry out such an attack on the USA if they had the means.
Sad, but true....
What’s instructive to me is that this DIDN’T mention the US. To me this shows that Al Queda knows it would be near impossible to do here, but they consider Britain an easier target. What they don’t seem to understand is that if they use a nuke, they’re committing political suicide, and even their ardent supporters among the Democrats would have an impossible time justifying that behavior.