No it's not.
Doug Jones like to have a word with you about how impossible it was to win Alabama for god's sake.
It's how she said it. It's a stretch to call it a swing state, but it's not impossible to win that seat, but it will require a perfect storm and the perfect circumstances, just like for Doug Jones in 2017.
Once again: maybe in a special, sure, but this ain't a special, & even in the event of the GOP nominating a Roy Moore, regular midterm turnout would probably be enough to push the GOP over-the-line.
Three things
A midterm is not a presidential election.
Secondly, candidate quality matters
Thirdly, Missouri ain't Alabama.
I think it's a bold take to say we can't win in some state, because of ... , because things aren't permanent and not set in stone. Things can always change. Sure, it's unlikely, at least in the short-term and whatever happens, the GOP is favoured, but it's not "impossible".