blue wall

Short definition from Wiktionary

Proper noun

1. 1
   A group of states known for consistently voting Democratic in presidential elections from 1992 through 2012.
2. 2
   A group of states known for consistently voting Democratic in presidential elections from 1992 through 2012: The three battleground states that were dislodged from the 1992-2012 group in 2016: Pennsylvania, Michigan, Wisconsin.
3. 3
   A group of Conservative-leaning parliamentary constituencies that are seen as shifting away from the party.

Noun

1. 1
   Alternative form of blue wall of silence.