Islam the religion is protected by the 1st amendment. Islam the political movement is forbidden by the 1st amendment.
There is no distinction - in the Koran, the Hadiths of the Sunnah, in any Islamic jurisprudence in history, or in any significant islamic dominion in history - between "islam as religion" and "islam as political movement".
go here: http://www.prophetofdoom.net/ltr.html
read. digest. understand.
Then tell me whether you still believe Islam is a religion and protected as such under the First Amendment.