Trump’s success has nothing to do with his policy proposals, issue stances etc. People are just fed up – pure and simple – with the status quo. Polls consistently show that overwhelming majority of citizens think the country is on the wrong track. Voting for any establishment politician only perpetuates the problem. So a vote for Trump is really a vote against the establishment.
Here’s what some of his supporters have to say. Note the diverse demographic: http://www.theguardian.com/us-news/2016/mar/03/secret-donald-trump-voters-speak-out

BTW, I am NOT a Trump supporter. I would seriously consider Bernie, given a chance. I strongly believe that if a system doesn’t work, it’s my duty to vote for a change. And if the system is fundamentally flawed, the change must be equally radical.