We all (as in the GOP and conservatives in general) acknowledge why Trump has done so well in the polls. And it has squat to do with "reaching out to racists or bigots". He's not part of the established hierarchy of the Republican party, and as such has no qualms stating politically incorrect verbage, that so many of the GOP are too afraid to say, for fear of being labeled a racist or a bigot. His assertiveness comes across to supporters as extreme confidence, and to his critics as supreme arrogance
While he likely would beat Clinton, and trounce Sanders, he's running the risk of alienating so many conservatives, that are truly geared up to vote Democrats out of the office, that they might just stay home. Case in point, while he rails against folks like Cruz, Rubio, and Bush, calling them liars for their claims that he "supports Obamacare", now he's on record as proclaiming his support of the mandate within Obamacare. Literally the cornerstone to Obamacare. You can't keep calling people liars, if you support the primary feature to that you supposedly oppose.
If he supports a Government mandate in having healthcare insurance, what's the difference between he and Clinton?..or Obama for that matter?