The Shutdown Might Be Hurting the GOP's Chances in Next Year's Election
But it's way too early to tell.
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.