The GOP has been eating itself since Obama (Tea Party and all) and has been on the brink of fracture. The fact it stayed together as much as it has for the past four years is nothing short of a miracle. But I also think Trump has damaged the GOP, on which the the democrats are seizing and using as a wedge. Brilliant political warfare for them.
If we're saying he did the damage because of his existence, sure. But the people who hurt this party the most were the neocons who thought they had control over the body politic and the people showed them otherwise.