So on the one hand, you need more data over more elections to see if there's correlation, but then that adds noise. At a national level, the parties have sub-parties within them where in consensual democracies they'd be separate parties, it's not a strictly two party system like you see in majoritarian democracies. And this is always in flux.
Another source of noise is just the nature of the 2016 presidential election. Possibly a better source to reduce noise? U.S. senate races. They're statewide like a presidential race, the term is 6 years, but the lack of national media hype involved in the campaigns makes them less emotional and the data might be more stable. The incumbency problem might make it useless.