Interestingly, I've been talking about that same question with some history nerds.
In 1974, Richard Nixon still had strong, base support among American voters and also members of both the Senate and the House.
The lever, as ever, will be when pressure from voters on those in less gerrymandered districts (and there are still enough of them...really!) make it clear that Trump is costing the Republicans votes. It may not happen until 2018, but it is trending that direction.