It just did happen here! We had the Boston Marathon, we had Ft. Hood shooting, we've had a string of "Sudden Jihad Syndrome" terrorist attacks in the USA.
I don't recall seeing a march as big as 250 people protesting Islam qua Islam. Do you?
So the answer is. Nothing. Nothing would happen here, we are even more passive than the Brits, who at least do have the EDL. Is there an American version, the ADL? No. Not really.
We have only a few voices in the wind telling the truth: Pam Geller of the Atlas Shrugs blog, and the recently deceased Lawrence Auster.
Very few in America have woken up to the reality of what Islam is, and even among those few not too many are willing to call for doing anything about it, like ending Muslim immigration and encouraging those who are Muslims to return to Muslim lands.