How far will the establishment go in its desperation to stop Trump?

[whiplash]

First they called him a clown
Then they called him disgusting and repugnant
Then they called him a racist, sexist bigot
Now they're calling him a fascist and comparing him to Hitler

I don't think you can go much further down the rabbit hole of desperation than comparing someone to Hitler.  Maybe they'll actually try to make the case that if we vote for Trump he will use WMDs against us?

And i should agree with some of their statements. He is really racist, even his father was a member of KKK in 1920s. He insults Asians, African-Americans and people of Hispanic origin. May be his racist sayings are more a political game to gain votes than his real position. But the fact remains.
Trump allows himself to insult minorities PUBLICLY. Why others can't do the same?

[whiplash]

Rigging the primaries would be electoral suicide, but you never know.

I think the GOP establishment would rather lose the election to the Democrats than see Trump win. 

While I don't think Trump is very likely to be elected next November, I can imagine that in the longshot scenario where that happens, there's talk of an "electoral college conspiracy", in which you get a bunch of faithless electors trying to throw the election to the House.  Even after he's won the election, it's not too late to nominate someone else! 

I do not think Electoral College allows Trump to win. This system has some 'loopholes' which were used during some previous elections. 538 members [whose number varies depending on the state] take the final decision.