I think the point is that there was also a dip with Dems. But IMHO, as someone who runs a lot of surveys for a living, the key it to look at the overall trend line, not one data point. And the overall democratic trend line over the past few years seems to have some noise in it that vacillates + or - 5% from the trend line.

The GOP line though… that feels like a change from historical trend line.

https://news.gallup.com/poll/507230/fewer-say-sex-relations-morally-acceptable.aspx