That's not clear at all. Far more of the natural Republican base (as opposed to the natural Trump base, although the two do majorly overlap) would be energized by the prospect of SOCIALIST to vote Republican, no matter what. As it is, Hilary has even gotten committed support from numerous, high profile, long-standing 'Pubs.
If you think the negatives against Hilary, which are in large part a result of an intense, well-funded, multi-decade campaign against both Clintons have had an effect, please come out of your bubble and think about what would be happening if that apparatus were directed against Bernie.
Don't you know that a Sanders candidacy would have energized the Koch brothers to part with Billions in the effort to defeat him?
People who think Bernie would win are in the mirror bubble of people who think Trump will win. For both, their supporters are deeply passionate, but they are not a majority of the electorate . . . that same electorate that gave Reagan and Nixon landslide victories and voted President Cheney in twice.
Spend more time in Walmart or at McDonalds and better get to know your fellow Americans, each of whose vote counts exactly the same as yours, before you confidently state that the entire electorate wouldn't be swayed by an extensive, shallow, attack ads campaign against the Jewish radical.
Recent historical proof? Try saying President McGovern with a straight face.
Need more? How about how the big lead Dukakis (an effing moderate!) had against the first Bush disappeared in the harsh glare of the national campaign. And you think Bernie would fare better? Wise up and come out of your bubble.
In conclusion, Willie Horton!!