What matters is turnout. In the "Like" and "Upvote" age, transforming those casual opinions into action at the voting booth is really what it is about.
I suspect Trump is using immigration and Kavanaugh as motivators to get people to the polls in the midterms. Certainly his base. It will also motivate the Left a bit, but he's played so much emotional rope-a-dope with them the last 2 years, I wonder how many shitlibs that aren't paid through Obama and Soros subsidiaries will actually bother to show up to vote, where it matters (contested seats).
The Left is great at organizing protests but they haven't shown themselves equally competent at organizing electoral victory. Certainly not in 2010, 2014, or 2016.
This isn't a "Trust Trump" thing, but I am not going to bet against a guy who has an air of Divine Providence and Serendipity about him.