lunatic fringe

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The fanatical, extremist, or irrational members of a society or group.

from the GNU version of the Collaborative International Dictionary of English.

• noun the members of a political or social group espousing extreme, fanatical, or seemingly irrational views.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The members of a political or social group espousing extreme, fanatical, or irrational views.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a political unit with extreme and fanatical views