Trump's "base" is not 90% of the Republican party, imo. I'd say that there's a faction of approximately 35% within the party who are die hards that won't even consider another candidate but Trump. Beyond that, it's possible to win over the hearts and minds of other Republicans, but only if you bring some quality traits to the table. Jeb Bush ain't cutting it.
The reason we're not seeing different behavior from Republicans right now is because there's no harm in playing a bit to both sides. The voters aren't going to remember anything 2 years from now, lol. So, if you're in a deep red district, you throw a little meat towards the Trump crowd, and if you're in a purple district, then you act like you're the voice of reason or whatever, lol. Then you wait 12 months and revise your personality accordingly.