Personally, I'm sick and tired of libs getting away with this kind of thing. I usually don't go in for suing people... But in this case, I'd go after the school and the police dept. I'd go for compensation deep in the 6 figures, and punitive damages equal to the sum of both the school district's and police dept's annual budgets...times 4 - since it'll be 4 years before he can make a similar statement at another Presidential rally.
Arrest under false pretense is all it takes. The arrest doesn't have to lead to a trial, or even an arraignment. If the charges are later dismissed or dropped by prosecutors, it doesn't change the fact that he was unjustly arrested in the first place. What the police did was to deprive this kid's of his rights under the color of law. That's a Federal offense, period.
L