The vast majority of Trump supporters will never change their minds on the issues at hand. Donald Trump has a way of gathering ignorant supporters (of whom, unfortunately, the USA comprises many) and convincing them he will "make America great again". Anyone who can be sucked in by such a highly ambiguous slogan is probably too ignorant to view the true issues with a rational mind.
Sanders can't convince Trump supporters to change their minds. Donald Trump and Bernie Sanders supporters do not stand for the same things. Sanders supports communism and increased government. Trump supports capitalism and decreased government. These two candidates couldn't be more different. Why would any Trump supporters switch to support Sanders?
Trump's supporters are of an entirely different breed than Bernie's. I think a more moderate candidate could possibly win them over, but I would say that the lion's share of Trump's supporters will be directed to whoever is nominated as the Republican candidate. Bernie's self-described moderate socialism will never fly with the hyper-conservative "anti-PC" culture that Trump supports.
Bernie Sanders, as appealing as he is to the mass, cannot and will not convert Trump supporters. Trump supporters are almost like a cult, following the man himself more than reason. The way for Bernie to get some of his supporters is to capitalize on opportunities when Trump goes so far over the line that he alienates part of his own followers. The problem here, though, is that his supporters seem so loyal that he can (and does) say anything he wants without repercussion from his followers.
I don't support either but if those are my only two choices, I would rather support Trump. I would rather vote for a turtle than Bernie. Insane socialist. Even worse than Obama.
All he wants to do is give stuff to the irresponsible and increase the sense of entitlement of those people.