The RNC has a difficult tightrope to walk, but it can be done.
What they have to do is focus on criticizing Hillary, and making Trump responsible for promoting himself. Because ads that attack Hillary, and what the Democrats will do if they regain control, can also help Congressional Republicans. And if it gets close to the election and Trump is looking to get clobbered, the GOP can play the "if you don't want Hillary to have total control over the entire country, you'd better elect Republicans to keep her in check" card.