Who is this Clark guy?
1. If Al Qaeda was able to purchase five or more "suitcase nukes", then any reasonably proficient nuclear physicist could get at least one to go off.
2. It is my impression that the Bush Administration believes that Al Qaeda has or might have nuclear weapons, due to their reactions that accompany elevated threat levels, including the deployment of portable radiation detectors.
3. It is my understanding that radiation detectors are indeed sensitive enough to pick up tritium in luminous wristwatches, at the ranges you might expect from roadside detection operations. In fact, there have been reports of people detained in similar scenarios. The radiation intensity (and therefore, detectability) falls off with the inverse square of the distance, however. If the detectors mentioned above were effective as described at a range of 50 feet, they would need to increase their sensitivity by a factor of approximately 128x to be similarly effective at the range of one mile.
4. The narrowly averted recent attacks on Britain and Amman, Jordan using chemical weapons (Osmium in Britian, unknown quantity, unknown material in Amman, quantity of 17 tons) may well be the basis for the recent increase in institutional and government sensitivity, and this may also account for Sen. Tom Daschle's reaction to a recent briefing, in which he stated that the information imparted was "extremely sobering", and almost "certainly not partisan". Then again, they may not.
5. Significant research has yet to conclusively determine the existance of any Soviet "suitcase nukes". The closest I have been able to find are the (existance contested) nuclear mines distributed to the KGB and Spetsnaz troops, in central Asia and eastern Europe. These, if they actually do exist, have shelf life problems, probably in both the neutron initiators (1970's technology) and any pumping mechanisms that might have been used to reduce the naked sphere critical mass of necessary core fuel for these high energy devices. The reported nominal yield of these devices was 0.1 KT.
Hope for the best, plan for the worst.