A historic cue in Gallup's wave predictions is self-reported enthusiasm. Take a look at those numbers historically compared to 2018:
1994: R+8
2006: D+12
2010: R+18
2018? R+3. (Forecast: no wave; Looks like 2002.) pic.twitter.com/WPcumTaOm4

— Robert Barnes (@barnes_law) November 1, 2018