Trump was actively torpedoing the party. The previous 15 years had culminated in this fucking clown being able to grift his way to the nomination while most of the party tried to back off of him.
No prominent Republican endorsed him until the 11th hour.
They thought he was going to lose even with Hillary fucking up.
They threw the email hail mary but Hillary not going to the mid west cooked her. She lost those states by such a slim margin.
But there was no momentum from Republicans as far as this being a united victory. Trump scorched every Republican candidate on the way up and continued to do so once he was elected.
They fall in line because they understand that they are only as strong as the sum.