"I thought the Republicans idolised him and everything he said, believed, and stood for. I had the impression that the Republican party believed Trump would win the next election by a significant margin. It seemed to me that only sane, normal people (ie not Republicans) saw him as a blustering, clueless, and dangerous buffoon."
When discussing the Republican party it's important to distinguish between the establishment and the base. To first approximation, the tiny elite in the establishment used the base's fear of Mexicans, Muslims, gays, a black president, etc. to get these suckers to vote against their own economic interests. For a while, this (along with gerrymandering) made the Republican party quite successful.
Now, Frankenstein's monster has gotten loose. Where establishment Republicans used dog whistles, Trump is openly labeling Mexicans as rapists and calling for a ban of all Muslims from the country. If you're a bigot, why settle for candidates who only hints at hatred? Why not support the orange, weird-haired big mouth saying everything you're thinking?
Luckily, enough Americans see Trump as the bigoted moron that he is. If he won the nomination not only would the Republicans lose the general, but the brand would be severally hurt, possibly for a very long time.
I predict the establishment is going to throw everything they have to make sure Trump doesn't get the nomination. They may be evil, but they're smart enough to realize a Trump nomination would be disastrous for them. A Trump presidency, unlikely as it is, would a catastrophe for the country and likely the planet. Maybe some establishment Republicans have enough humanity in them and are opposing Trump for this reason alone, but I have my doubts.