Arresting al-Sadr is a big, big risk, in that it assumes that the US can discredit the one person in Iraq who dares to oppose the US. Not only could it foment a great deal of unrest, as Sadr has over a million supporters, but it could also encourage those angry at the US presence in their country to follow someone a whole lot smarter and more prone to violence than al-Sadr. Sadr becomes a martyr or political prisoner, and a dozen other radicals take his place...
Under the circumstances, 30,000 additional army reservists doesn't sound like all that many. It certainly doesn't sound like security.
