I'll try to drag this away from the standard partisan insults and back to the actual point.
Trump is, to say the least, "fluid" on several issues. But I think it's fair to say that illegal immigration and jobs/trade are two pretty important issues for both parties.
Hopefully some Trump supporters will chime in to discuss their concerns about the question posed in the OP. And I'd also wonder what a knee-jerk reaction to those issues would actually look like.
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Have you ever seen a large segment of a party say anything along the lines of “We will not vote for our nominee” or “We are leaning away from voting for our candidate” or “We will not be supporting our candidate this fall”?
I haven’t and I’m pretty plugged in on elections.
Remove Robert Dole from the equation. The GOP has had 5 pretty different men run for it’s nomination.
Ronald Reagan: Former Governor, Movie Star. Light on details and policy specifics. Great communicator. Father figure. Lightly Partisan
George Herbert Walker Bush: VP. Party stalwart. Heavy on details and specifics. Terrible Communicator. Father figure. Partisan
George W. Bush. Former Governor. Unremarkable. Light on policy details and specifics. Terrible Communicator. Likable. Partisan
John McCain. War hero. Instinctive politician. Had bad luck of running into a buzzsaw/Bush fatigue. Likable. Moderate
Willard Mitt Romney. Trust fund baby. Former Governor. Terrible Communicator. Bad Campaigner. Unlikable. Moderate
The GOP has gotten behind each of these men despite their differing approaches, backgrounds, temperaments, etc… The GOP would have gotten behind Donald Trump if he hadn’t acted like a horse’s ass for so long.
I doubt his policy pronouncements are that unpopular with many in the GOP. If Kasich had the same policy profile and the votes, there would be no “I will not support that man” to speak of.