In case you hadn't been following all of the smaller special elections this was for a state senate seat in Wisconsin's 10th District. One that Trump had won by 17 points but just went to Democrats by 9 points. Gov. Scott Walker has labeled it a "wake-up call" to the GOP and its supporters.
Some important points from the linked article:
- Republicans far outspent Democrats in this race
- The previous Republican incumbent had won the seat with 63% of the vote
- Unlike with Moore, the Republican candidate was not particularly weak
- Schachtner was a model candidate for the area with deep roots to the area and a message that resounded well (read as just left of center)
Analysts are sometimes skeptical of projecting special elections results onto midterms ("special elections are special" is the phrase I hear most) but there is mounting evidence that the national sentiment is more against the party holding the White House than is typical.