fever swamp

Short definition from Wiktionary

Noun

1. 1
   An area of stagnant water and hot temperatures that acts as a breeding ground for disease vectors such as mosquitos.
2. 2
   A group of political extremists or an area that is dominated by them.
3. 3
   A set of extreme and crazy political positions.
4. 4
   Alternative form of fever swamp: Disease-ridden swamp.
5. 5
   Alternative form of fever swamp: Group of political extremists.
6. 6
   Alternative form of fever swamp: Extreme political positions.