Last year a massive study on the happiness of high school seniors was published. The study looked at 86,138 high school seniors from 2005-2018. It found that unhappiness was on the rise among these students:

Some other trends do appear. Men are happier than women, conservatives are happier than liberals, and ideology matters more than gender. Remember, we’re not looking at the same people as they’re aging. We’re looking at groups of 12th graders over time. The gap between conservatives and liberals has widened. That’s mainly because 12th grade female liberals are become unhappier faster than others at that age.

This isn’t a one-off thing among high schoolers. There’s been a happiness gap between conservatives and liberals across all age groups and over many decades. The General Social Survey (GSS) has been conducted in America every year or two since 1972. Republicans have always been happier than Democrats. Regardless of which party was in power.