For the past 40-plus years, the National Science Foundation has funded something called the General Social Survey — a poll gauging the attitudes of hundreds of Americans on a consistent set of issues. Do you support gay marriage? How do you feel about women in politics? Do we spend too much fighting crime? That sort of thing. The results are broken down by various demographic groupings, allowing for a fascinating look at how America has evolved.

Consider, for example, attitudes about the press. It is by now common knowledge that confidence in the press has waned over time. Every year, Gallup releases an assessment of how much Americans trust the media; it has been sinking lower over time. Thanks to the GSS, though, we can see a longer trend — and when, exactly, that trust started to evaporate.

In the GSS, the question is posed as being about how much confidence the respondent has — a great deal, only some, or hardly any. In the 1970s, respondents generally said “only some.” But in the 1990s, patterns shifted and “hardly any” shot up. In the 2016 GSS, released this week, “hardly any” was the response of a plurality of people.

Notice the pattern of “hardly any” since 2004, though. During presidential election years — marked with vertical lines — the “hardly any” response is up. During midterms, it’s down.

Why? Republicans.

While confidence among members of both parties has declined over time, the Republican pattern is interesting: Up during a presidential election, down during the off-year. Only in the 2012-2014-2016 period does that hold for Democrats. (Notice, too, the increase among independents over that time period.)

Notice, though, where that variation comes into play. Conservative Republicans are pretty consistently skeptical of the press. Moderate Republicans, though, see big swings from cycle to cycle. There are fewer of them, so variability can increase more easily. But much of that cycle-to-cycle swing is clearly from these moderates.

There are a number of unanswered questions here. Why the sudden surge in distrust in the early 1990s? Why are moderate Republicans more likely to distrust the media during a presidential election year? Your theories are welcome.

One question we can answer though: There doesn’t seem to be a link between education levels and confidence in the press. Overall, those without a college degree are generally more likely to have confidence in the press. When broken out by party, education level doesn’t make much difference.

These data also suggest something else. The candidacy of Donald Trump and his constant assertions of media bias don’t seem to have made Republicans significantly more skeptical of the media than they normally — or than they would normally be during a presidential election year. Instead, it seems safer to assume that he was simply playing to their existing concerns.

The General Social Survey was funded primarily by the National Science Foundation and conducted through in-person interviews with a random national sample of roughly 1,900 adults in the spring of 2016. Overall results carry a margin of sampling error of roughly 2.5 percentage points; the error margin for subgroups is larger.