It’s nothing new. Since it’s inception, the General Social Survey has inquired about respondents’ self-reported personal happiness. In every single year, Republican happiness has averaged higher than Democrat happiness has:
It doesn’t seem to track much with which party controls the White House, one of the few things about the contemporary United States that would make the nation’s founders happy. During Republican presidential administrations, Republicans have a net happiness score averaging 14.1 points higher than Democrats. During Democrat presidential administrations, Republicans’ net happiness score averages 12.4 points higher than that of Democrats, a modest difference.
Looking at congressional control might reveal a stronger correlation. In 2012, during the heyday of the Tea Party, for example, Republican happiness shoots up while Democrat happiness dips a bit. Notably, TDS isn’t detectable in the 2018 iteration of the survey at all.
GSS variables used: HAPPY(1)(3), YEAR, PARTYID(0-1)(5-6)