Poll analyst extraordinaire Sam Wang thinks that things are looking fairly bleak for Republicans right now:
PPP surveyed 24 Congressional districts currently held by Republicans. They asked voters to choose between their current representative and a generic Democrat….The swing was toward Democrats for 23 races  and toward the Republican for 1 race.
….Since the election is over a year away, it is hard to predict how this will translate to future seat gain/loss. If the election were held today, Democrats would pick up around 30 seats, giving them control of the chamber. I do not expect this to happen.
….In a followup series of questions, PPP then told respondents that their representative voted for the shutdown. At that point, the average swing moved a further 3.1% toward Democrats….That would be more like a 50-seat gain for Democrats — equivalent to a wave election. An analyst would have to be crazy to predict that!
I would echo Wang’s caution. It’s quite normal for Democrats to perform well in generic congressional polls 6-9 months before a midterm election, so this probably doesn’t mean much. As for the shutdown, I think it’s an open question whether that’s still going to be a live issue by next November. It might be! Or it might have been completely forgotten. I just wouldn’t put much stock in this either way.