>>520625577 (OP)
Based on numbers, Democrats were viewed as more responsible for the shutdown by about 3 points or so. However, Trump not being on the ballot was the bigger issue. The "why should I vote when we have the Presidency" mindset kicked in. Merge that with already apathetic voters who basically need to be spoonfed why elections are important every time one pops up AND the fact that said voters vehemently reject early voting and mail-in ballots (while also not being able to actually vote on Election Day depending on others to overwhelm the ballot boxes), and you have what happened.
These wins were in blue states by and large so these aren't that surprising, but historically the voters of the part who holds the federal government shits the best when it comes to local elections because they think it doesn't matter (because they have the federal). Also the self justification of "surely we won't vote for that guy, I don't NEED to vote" popped in too. Shutdown wasn't the issue, apathy was. And apathy was fueled by Trump not being on the ticket.