You have to be careful with special elections. People tend to over interpret them. But they can be warning signs. And House District 97 in Missouri is one such warning sign. That state house seat went for Donald Trump by 28 points in 2016. During the last regular election, the Republican incumbent, John McCaherty, had no Democrat challenger.
But McCaherty resigned to focus on a different race. His resignation forced a special election where a Democrat just beat the Republican by 108 votes. There were two other special elections wherein the Republican easily won. But what makes this race unique is that it involves a suburban area that swung heavily for Trump. If Democrats keep picking up these suburban areas they will not only take back Congress in 2018, but they'll be well on their way to taking back state legislatures in the run up to redistricting in 2020. This also raises the question of just how vulnerable Claire McCaskill is in Missouri.