There's no reason to think they won't, once November rolls around.
As long as the President is active, and the economy keeps growing, the GOP should be OK in November—despite themselves.
There's no basis for presuming November will be a bloodbath—not based on a couple of races.
It's simply too far into the future, and I can't believe that so many around are yet again falling for the gaslighting from the Propaganda Media.
Taking the entire "special election" cycle as a whole, the GOP is doing fine. The Roy Moore situation was a special case, and the donations are strong in general.
If the Republicans get out the vote, they'll perform adequately, and there's no excuse for 2016 GOP voters not to get out and vote in November 2018...
...”and there’s no excuse for 2016 GOP voters not to get out and vote in November 2018...” Unless, of course, they have died, since 2016. Dead voters vote Democrat, only!