@ Kino: Moving the goalposts now? >:O
Would saying "Accio President" work?
Another thing: the shield charm can deflect physical objects. It is possible to enchant articles of clothing to provide a constant effect. There's also the time, in the movie at least, where Dumbledore turns falling glass shards to sand with a shield spell.
I think with this in mind, it's safe to assume you could indeed effectively make a wizard immune to conventional firearms.
Before I go, just wanted to throw one more thing in: So far we've pretty much been talking wizards vs. the US. How would wizards vs. Third World country without all the fancy tech and money go? Could wizards take over say, Central Asia and control the place with puppet regimes (possibly with the imperius curse)? What about India * or Pakistan, both of whom have nuclear weapons? (EDIT: They don't necessarily have to aim them at the US either; what are the US's major trading partners?) Is there any area of the world besides Europe that would affect the United States very badly if it were to be destabilized?
edited 28th Nov '10 11:53:12 PM by melloncollie
Because its fun
The British population is.
But look at how many people turned up to the Quidditch World Cup.
Then consider that;
not everyone likes Quidditch;
and there were only so many tickets.
So the population is even larger than that.
Still tiny, but not ridiculously so.
There are too many toasters in my chimney!Only four, if one of the SS guys is Kingsley Shacklebolt under polyjuice, the original being transfigured into a bedside table, in his bedroom.
But none of them were forced to secretly do a Heel–Face Turn / Face–Heel Turn by Imperius, casted by a SS guy.
edited 28th Nov '10 11:51:43 PM by EternalSeptember
I imagine it would be easy to figure out if an authority figure starts acting out of character, though I doubt you could protect yourself.
Also, on the apperation business, I forgot the simplest method: teleporting the magical equivalent of a bomb to the target. I imagine it wouldn't be out of the question to enchant something to go off with a blasting curse.
I gotta wonder what would happen if the wizards through open a door in the Department of Mysteries and let the Power of Love out. Would they be able to harness it to use against their enemies, or would it be a case of Wild Magic?

How fast can the Pony Express deliver a message with today's roads, I wonder...