The conventional wisdom about midterm elections is that the party whose candidate lost the last presidential election gains seats in the House of Representatives, and perhaps the Senate too. Seemingly, all Democrats had to do was behave themselves, point to places where the Republicans dropped the ball, and they'd win extra House seats for sure, maybe even a majority.
This, it turned out, they were unable to do. Democrats tripped over the "behave themselves" part of that Rx, and went nuts over Judge (now Justice) Kavanaugh. Some small fraction of 1% acted up, screamed, cried, got arrested, and clawed at the Supreme Court doors. Meanwhile their senators on the committee acted crude, rude and sneaky. Given the 24/7 news cycle, cameras were there and the country watched the melt-down.
Now from all sides we hear of the "Kavanaugh Effect" as polls show opinion trending toward the GOP. Who knew the rest of us wouldn't find the spectacle of feminist protest and senatorial melt-down edifying and encouraging? Some Democrats - who could have won - will lose because of their supporters’ on-camera, self-defeating behavior.
The temptation to look about for a hoisting petard is very nearly insurmountable.